Hi, As I understand it 1968 and 1969 Mercury 650 motors are pretty much the same. I also under stood 1970 and 1971 are the same . Apparently the only difference between the years is that in 1970, 71 they used a 2.3 to 1 gear ratio v 2.1 to 1 in 68,69? Is this correct.? Is there any reason to use on year over the other if all other things are equal condition wise? More dig but slightly less top end? Thanks ,Keith