You must change the pistons. The crank and pistons are the difference. You can keep the rods. It is possible the earlier year 429 will have a .020" shorter deck height than a later 460, and the increased volume of the longer stroke would have a very small impact on compression. But you have to buy pistons.. so pick out what you want. I did this when rebuilding a 70 model 429 just because it was easy. The only increased cost was finding another crankshaft. I would highly recommend balancing it when done.