The AMC 304, 360, & 401 all share the same block per say. The internals obviously will be different due to motor size but things like the valve covers, oil pan, water pump, timing chain cover, and intake manifolds are all interchangeable. Flywheels, flex plates, harmonic balancers are not as the motors are externally balanced and vary for each engine size. For the early AMC motors such as the 390 I am not positive but may still have some interchangeable parts. I know the deck on the 390 was raised to make the 401 and the early AMC V8 heads had more of a dog leg bend in the exhaust port than the later versions.