Electric shift ended in 1977 if I remember correctly. After that came a hydro-mechanical shift up through 1980 when it switched to a full-mechanical shift with an ignition cut-out to relieve drive force & allow the clutch dog to slide out. Each shifting mechanism improved over the previous in various ways (or at least changed things). I had a hydro-mechanical in a 1980 boat previous to this boat & never had a problem with it but I've read the full-mechanical is more desirable and reliable. You'd need a completely different outdrive to switch between electric & either of the mechanical shifting (along with a remote, etc.). I'm not sure if a drive change is required to go between hydro-mechanical & full-mechanical, but full-mechanical certainly requires some additional parts to handle the ignition retarding mechanism.
So I guess the question is why do you ask? What's wrong that you're considering switching?
