As stated it all depends on what your willing to spend, but I would go a step further and ask what does the car have now.
I know it does not have a motor, but what about the rest of the drivetrain? My reasoning for this is that if the car was originally a 318 or a /6 powered car then it will be a bit more work to make the car perform as well as a 340 or big block car. Even the 2 BBl 383 cars had larger torsion bars, heavier duty brakes, bigger radiator, larger rear ends, etc. If this is a /6 or 318 car with the 18" radiator, 904 tranny, and the 7 1/4 rear end (grenade!) then there is alot more to it then sliding a BB, Hemi, or even a 340.