[78 WS6]

I am wanting to put a Pontiac 400 in a 69 GMC SWB. Moreover, I want it to appear factory, so instead of just crafting mounts that would obviously not appear factory, I would like to find frame stands that would accomplish my goal. I believe I had read somewhere of an application that would do this but can't remember what they are. Any help out there would be appreciated.
THANX!

[steve25]

It's gonna be hard to make it pass for a factory Chevy motor when the Pontiac has its Alt and starter on the opposite side.

[78 WS6]

I'll assume you are too young to get the point. In 69 GMC was in its V6 era 305 & 351 cu. in. In earlier days when GMC had V8s they were not Chevy but Pontiac. So the point here is a "what if" 69 GMCs still had V8s and were still Pontiac. All the Chevy/GMC twins came later.

[unruhjonny]

I've read of these kinds of swaps over again;
IIRC you need to find and install block side, and frame side mounts on the engine, place it in the engine bay, then determine where the cross member needs to have the frame side mounts affixed... after that, it should all fall into place.

[steve25]

No , I am not too young as I was born in 55 thank you, lol!

[Schurkey]

Originally Posted by 78 WS6

In earlier days when GMC had V8s they were not Chevy but Pontiac.

Pontiac, and Olds. Both supplied V-8 engines for GMC trucks in the '50s.

Chevy got larger V-8s from Buick in the fifties..

[Ducks Goat]

My sister has a '70 GMC with a 455 in it that our dad installed and he is currently putting a 428 in his '68 GMC. I think he used factory mounts or some form. I'll try to find out tomorrow what he used.

[Ducks Goat]

Oh BTW I think it's in the 70 GMC assembly manual, anyway there is a page that shows a real Pontiac engine installed. I'll try to find that page as well.

[Tom Vaught]

I have seen several Later Model GMC vehicles with Pontiac Engines installed by their owners. In all cases the owners were very happy with the engine swaps.
Typically they were the 455 engines with the T-400 Trans swaps and in a few cases (with guys that built Transmissions) they installed a Switch Pitch converter along with the proper trans.

Tom V.

In 1971, a Pontiac Guy named Ralph Piper had a early GMC truck with a 1965 Tri-power engine and good tires that would run 11.70s at US-131 Dragway in Martin Michigan.

[sdbob]

I installed 71 400 with long tailshaft m40 in my 74 2500 Chevy(350,m35) 30 yrs ago. Used if I remember 74 f body frame mounts. Almost bolt in existing holes. Crossmember might be redrilled.Cut driveshaft. Used existing linkage,all I had.Changed starter wiring. Only problem i couldn't trans manually in low. I guess if I worked it out I could. It was a weekend swap. Needed truck for work.Other than that worked fine. Towed way better with 400 torque.Had heavy utility body also.

[77 TRASHCAN]

I will tell you what I know, it might be helpful...

Pontiac's started using clam shell motor mounts in the mid 70's. The clam shell mount bolts to the cross member, my T/A has such mounts

The 67-72 pickups and 73-87 pickups have steel brackets (or stands) that bolt to the cross member and the top of the frame, on each side.

The 67-71 pickups used a mount that bolted the the engine (a rubber mount sandwiched between 2 pieces of steel thin plate). 72 small block pickups used same type of mount. These specific pickups just used the 2 pieces (mount and stand) to install engine...

72 big block pickups used the clam shell mount. The frame stand was drastically different than the 67-71 stands and the 72 small block stands...

On the 72's the clam shell mount bolted to the frame stand. A steel receiver piece bolted to the engine, it sat down over the clam shell mount, one long bolt holding the receiver to the clam shell mount (went through receiver and slam shell mount). 3 pieces...

73-87 pickups used a very similar mount system to the 72 big lock setup, but I am sure the frame stands are different on the 73-up pickups.

The engine brackets on Pontiac's MAY be able to be attached to a clam shell mount setup on a pickup, MAYBE. There were different engine brackets on the Pontiac engines. I do know that the "F" body brackets are slightly different from the full sized Pontiac's, slightly different...

The 72 big block pickup frame stands are scarce not easy to come up with. I believe the 73-87 pickup frame stands MIGHT work on your 69 pickup (millions of these were made, I believe small and big block stuff was same from 73-87), but I have not tried this...

I have 67 and a 68 Chevrolet pickup, both C-10's. Plan to use 72 big block mount setup on both, if I can find parts...clam shell mount setup is only way to go. My 68 is an original big block pickup...yes I still have original engine, and all pieces...

Questions?

[The Champ]

Originally Posted by 78 WS6

I'll assume you are too young to get the point. In 69 GMC was in its V6 era 305 & 351 cu. in. In earlier days when GMC had V8s they were not Chevy but Pontiac. So the point here is a "what if" 69 GMCs still had V8s and were still Pontiac. All the Chevy/GMC twins came later.

That info doesn't jive with the 1969 GMC Order Form:



Looks like either a 250 or 292 ci inline 6 or an assortment of L code V8's (LS8, LS9, L47 and L56).

My dad sold GMC's from 1963 until 1995.

[unruhjonny]

... I was guessing that '78_WS6' made a typo;
I believe that from at least 1967 GMC trucks used chevy drivetrains;
My cousin owned a 1969 GMC with a 396 - and I have understood that the same generation of GM trucks all used the same drivetrain.

[78 WS6]

Thanks for the reply that addressed the question. I am now doubting some of the facts that I remember. Regardless of whether I've got the facts straight on GMC V6s this is the way I have planned to build this truck for a long time. I have no intent to try to tell anyone it came this way, but rather only have it look as if it could have.

[78 WS6]

Originally Posted by 78 WS6

Thanks for the reply that addressed the question. I am now doubting some of the facts that I remember. Regardless of whether I've got the facts straight on GMC V6s this is the way I have planned to build this truck for a long time. I have no intent to try to tell anyone it came this way, but rather only have it look as if it could have.

This was an answer to Duck's Goat

[77 TRASHCAN]

Originally Posted by 78 WS6

Thanks for the reply that addressed the question. I am now doubting some of the facts that I remember. Regardless of whether I've got the facts straight on GMC V6s this is the way I have planned to build this truck for a long time. I have no intent to try to tell anyone it came this way, but rather only have it look as if it could have.

I would like to try to put a 455 in my 67 C10, but have an awesome 406 cube small block on hand for it....

IF, IF it was me, doing this...I look for the Pontiac engine brackets, either "F" body, full size Pontiac or Grand Prix brackets. (I know that the full size brackets are ever so slightly different from the full size brackets) I do not know anything about the Gran Prix engine brackets? Anyone?

Then I would try to obtain some 73-87 Chevy pickup frame Stands. The clam shell mounts can be purchased from a parts store. I would bolt the frame stands in. Bolt the engine brackets to the engine AND bolt the clam shell mounts to the engine brackets....

THEN...lower the engine and trans into the engine bay carefully and see where the clam shell mounts line up on the frame stands. After carefully making sure the engine is level and that the clam shell mounts are safely contacting the frame stands.....see where everything lines up...if the clam shell bolt holes don't line up with the frame, you might be able to make holes in the frame stands.....

OR, the best way may be to install engine brackets, clam shell mounts AND frame stand ALL to engine, then lower it all into engine compartment, see where that goes...

The V-8 engines in the 67-72 pickups had the frame stands bolted to the forward 2 holes on the frame, and one bolt to the cross member (6 bangers used the rear most 2 bolt holes). I get the feeling the new holes may need to be drilled to use the 73-up frame stands...

The only unknown as fay as I can see...mentally is where that 73-up frame stands bolt to...when using a Pontiac engine

If you are not a member on the Chevy pickup website, it is: 67-72 Chevytrucks.com You could place a want-to-buy ad there, to get the frame stands, BUT you have to be a paying member there to do so...it's not much $$$ yearly

[78 WS6]

I guess I should mention the GMC currently has the 305 V6.

[77 TRASHCAN]

Your frame and cross member should be the same...I doubt having that original engine will matter.

Sounds like the "OR" method might be best to start with.

[Baron Von Zeppelin]

Originally Posted by The Champ

That info doesn't jive with the 1969 GMC Order Form
My dad sold GMC's from 1963 until 1995.

Did your Dad sell GMC's in Canada ?
Thats a GM of Canada order form

Just wondering because most all GM/GMC products built in Canada prior to 1970 had Chevy drivetrains.

Originally Posted by 78 WS6

I guess I should mention the GMC currently has the 305 V6.

Who made the 305 V6 engine ?

[Baron Von Zeppelin]

From Wikipedia

The 304.6-cubic-inch (5.0 L) 305 had a 4.25 in (108 mm) bore and 3.58 in stroke (90.9 mm). The 305 V6 was GMC's standard pickup truck and Suburban engine from 1960 to 1974, and was one of the first V6 engines produced by an American company. The 305A was equipped with a single barrel carburetor and produced 150 gross horse power at 3600 rpm and 260 gross torque at 1600 rpm (i.e. measured without air cleaner or accessories in an ideal environment). GMC also made a B,C,D and E version of the 305 v6. The E version producing 165 gross HP at 3600 rpm and 280 gross torque at 1600 rpm.


Looks like that was the Base Engine (no up-charge) for US production models

I have never seen one , that i can recall.
Most probably had up-charge optional engines in them.