I can tell you from experience, that if you want to enjoy the car because it's a convertible....don't get too carried away with the motor. When I built my 71 Challenger conv. back in 92, I put a beast of a 340 six pak motor in it. Sure it ran like a gut shot cat, but it was not much fun just to ride in. I ended up taking the hot 340 out, and replacing it with a mild 360 around 94-95. It's still in there, and the car is MUCH more enjoyable without all the thumping,shaking and having to hunt race gas. If you build a stroker, build a mild 451 that you can run big block HP manifolds on, and get one of Jamie Passons new 5 spds to go behind it. Good luck