I need a replacement lower unit for an 83' Johnson 50hp, model J50ELCTA. It is a 20" shaft. I would really like for someone to tell me the range of year and horsepower that would be compatible for my engine. I think a 1979-1991, 40-60 hp will work, but I want to be for sure and I know there are some really smart guys in here that might be able to help me in this area, Thanks a million!