Cool Runnin,
Like previously stated if the engine is original to the car then the car will be worth much more with it. But if not then sky is the limit. It depends on how much power He wants to have. You can build a 383 with very good power and torque, but it will cost approximately the same to build the 440. Except if your going to put expensive parts in them. It does cost more to build a mopar, but it doesn't take as much to make respecable power and torque. People like the 67' to 71' motors better because they forged cranks. The newer ones have cast. You can still build them for good power though. If it were my car and the motor wasn't original I would build the 440.