I have an '81 Johnson 50hp 2 cyl outboard and it runs really well, but after installing a used lower unit ('75 Evinrude 55hp) I've noticed it doesn't go into reverse as smoothly as the forward gear it kind of makes a chattering sound through the gear shifter. I have replaced the cables, the gear shifter and adjusted all the linkage as per my '81 OMC shp manual states to no avail. I need to know what years of production & horsepower of Johnson/Evinrude lower units will interchange with my outboard because I may need to have a good used spare and the cost of just putting in a clutch dog or reverse gear will undoubtedly cost more than a used lower unit