getting a car

If it's an original 340 duster, you might want to keep it stock. Worth more than swapping in a different drivetrain. As OP said it's been in a garage, and he knows nothing about it. If it's a slant 6 or 318 car, then do whatever with it, but a 340 duster, I'd restore to original condition. Heck, the car may already be in good condition. He hasn't seen it yet, so everybodies going on speculation.