Aside from the bolt pattern when mounted to the engine, is there a physical difference internal and/or external between the two trannies?
Guts should be the same. 6" tail shaft to 6" tail shaft. which is normally used on A-body and F - body cars.
You can also get a dual pattern TH-350 that is BOP and Chevy. I have a few of them myself. Good for whatever project you get next lol