[Bill Hanlon]

If a GMC block, the engine serial number will start with the engine size, 288, 316, 347 or 336 depending on the year. And no, I can't tell you why GMC advertised one cubic inch larger than Pontiac in 1955 and one smaller in '56

[Safari Larry]

Originally Posted by Rachelsdad

This transmission has two cooler lines running forward, which went to an aux cooler, zip-tied to the radiator supports in front of the radiator. The lines are dry, as was the cooler when I removed it. Obviously, none of that was as delivered with the car when new. Again, I'll know more about the transmission toward the end of the week.

The trans cooler line running to the front makes me wonder if you may have a 57 transmission. 57 Pontiacs with hydramatic had two cooler lines running to the front and connected to the lower radiator for trans cooling (and heating when cold). 56 cooled the trans differently and did not have lines running to the front and did not have that feature in the radiator. The aux cooler may have been used in your 56 to get the trans cooling similar to 57. If that's the case, there is a problem with how it was done. Aux cooler in front of trans will cool but will not heat when trans is cold, not good for cold weather conditions. You'll find out soon what year the trans is.

[Rachelsdad]

Bill, thanks for that extra info regarding the GMC identification. As we say in the vernacular, who knew? :-)

Larry, I just had my radiator re-cored. It's definitely a '56 (no trans cooler in it). Indeed, there is a lot which has been done to this poor car over the years that none of us would have done (I won't belabor this thread with descriptions of the rat's nest I cut out from under the dash - and still not done; I'm really looking at a new harness, but I needed to get the spaghetti out of the way so I could remove the other components). The trans cooler was just a "minor" mess.

Stay tuned for tales of my next adventure under the hood and under the car.