OldBogie (as always) is right! I can't speak to the various and sundry bolt patterns, but I can speak to the transmissions from 1956. As a kid in high school and college, I went through about 1 a year. And I was never brutal. They just seemed to crumble internally. The manuals, anyway. Dunno personnaly of anyone having trouble with the automatics. But, then again, those engines were only about 200-225 HP. A 390 would give it a lot of extra exercise. Perhaps a C6?