i have a 1977 K-5 with a 1980 1 ton 454 and the stock TH350 transmission. The flywheel is now cracked and i have to replace it. While looking online it is apparent that the engine and the transmission don't match up when using sites such as napaonline.com when it asks for the make/model/engine/transmission details. Either i get a TH400 transmission flexplate with the 1980 454 or a TH350 transmission but then my choices are only the 305V8 engine. So my question is...what flexplate do i choose and are there drawbacks to this engine/tranny combo as far as selecting a flexplate? Right now i just plan on getting a new version of the cracked flywheel when i remove it.

I have very little knowledge of engines and drivetrains for trucks so forgive me if i am making a big deal out of nothing.

 

A big block with a TH350 is not a favorable combination, that is for sure.

The good news for you is that you just need to get the proper flex plate for the engine. If you want to be sure that the part is correct, remove the old one and carry it to the parts store with you once they have the replacement in hand. You should not drive the truck with a broken flex plate anyway.