I am running a 1990 Mustang 5.0 (302) with the stock fuel injection and the AOD trans and it's a good cruising combo for my '56. Trouble is, you don't see many low mileage versions in the yards anymore as they're getting kinda old.
What I'm planning for my '57 is a 4.6 or 5.4 Modular eng./trans out of a later Ford product. Many more to chose from nowadays.