Well, it depends on what year 750K you're talking about. The 77/78 K models were dimensionally the same as the A model tanks, the only difference being that the A tank had the fuel level sending unit for the fuel gauge. If you are looking at a 76 or earlier K tank, then you might ask (or search) about installing an early K tank on a later K frame. I know that it has been done, but I think you end up with a gap between the tank and seat that would have to be addressed (or not).