Here is a few more things to add to this post that might channel the conversation towards a reasonable build.
Why not look back to the past? Check out the March 1969 edition of Super Stock and Drag Illustrate. The story? Royal Pontiac's F/S 350 HO Super Stock Firebird. Hmmm. 12.59 @ 110.29 on a cold day. A 350 is not worth building?
Again, Super Stock, where the compression was 10.5, the cam a factory Ram Air with 288/302 duration, 4.14" lift. Factory cast crank, rods, and replacement forged pistons. 4-bolt main caps were added. Of course, the engine was blueprinted. Weight of the car was 3350 pounds where the light weight of the Firebird makes a difference as does 4.33 gearing.
Does anyone here think 12.59 out of a basically stock 350HO is not impressive?
I have to preference this by saying I have no expereince in building up a 350 Pontiac. I myself do have 3 of them and hang on to them as a possible means to build a healthy 350 at some point.
My concern here would be the mention of the 1975 and up blocks being weaker like the 400 later blocks. Never heard this, but never worked with these later blocks. If true, then I would not use a stroker crank.
I would add ARP main cap studs to whatever stroke I selected and wouldn't go with 4-bolt main caps.
Purchasing the bottom end parts individually usually costs more than buying a kit. Keep in mind shipping cost when you piece it together, but it is an option. The Butler 4.25" stroker kit seems to be the best price/option and you are ready to roll if you go that route.
Your head and cam choices will be important, so you will be spending more $$, or the stroker route will be for nothing as the engine runs out of air and RPM. The engine needs to breathe so you will want to invest in prepping the iron heads you have to include some port/bowl work to get flow up above the stock numbers - so if you don't have a machine shop/engine builder who can do this correctly, then you may want to send them out. You can also buy a set ready to go as most of the big name Pontiac builders offer these.
Keep in mind that you probably have the 6x-4 heads, 93.5 cc's and 2.11/1.66 valves. Compression shows to be 7.6 on the 1975 350. Not good at all for performance. Playing with the Wallace Compression Calculator, milling the heads to get 90cc chambers, getting a zero deck clearance, and .039" head gaskets, I get 7.87. Going to a 4.25 stroke gets you 8.79. Both not the best at all. You want to shoot for 9.0 compression in my opinion, but that means about a 75 cc chamber with a zero deck height or any of the Pontiac high performance heads with 72 cc's and the typical factory deck height of .015" down in the hole. But the 8.79/stroker combo is workable using a tighter 110 LSA selected cam and building cylinder pressure.
You can obviously increase compression with smaller chamber heads, but I am taking into consideration that you want to keep all your original engine parts to include your heads.
So let's begin with that and see where it takes the forum members.
What I don't think has been mentioned, is there a budget that needs to be applied to this build?