Engine Mount Differences?

Seems to me I remember the FSM listed different mounts for some 170 applications. I have no idea what the difference is. I have never seen "aftermarket" listing for the different mounts. My cars are all 1964-1966 "A" bodies, and I run 170's, and 225's. All use the same "K" member, engine bracket (metal part), and insulator (rubber part)