3-speed help

Hi guys, I was looking to find a 3 speed for my 1972 duster twister because that is what came factory, what should I be looking for? I was told it should be long shaft instead of a short staff, also could I use the shifting linkage from a 4 speed to a 3 speed? I’m guessing they are going to be different lengths but that’s why I am asking, thank you again!