65 and 64 valiant parts interchange

Why do you have to change the valve bodies i'm puttin a 65 model in my 63 and everything from the 63 everything looks the same and the cables hooked right up
Use the 63 valve body, or swap out the "manual" valve, and "comb". The 65 valve body has 6 detents, where the 63 valve body has 5 detents