between a 396 engine and a 454 engine?? I'm in the process of buying a 1969 camaro, and the owner claims the engine is a 396.

 

there are casting numbers on the block that will tell you what size motor they where used for thats one way

 

In addition to the info in the link below, look for a number stamping pad above the timing chain cover.
Also check the engine's partial VIN against the last six digits of the car's VIN. If they match, the engine is automatically a 396,
as that's the big block GM put in your car (SS model). Chevy Camaro FAQ Casting # 3932388