[THEFERMANATOR]

I know that there were some different ignition systems used on them early on(non magneto styles). I'm not really up on the old loopers myself, only the 90 degree engines. But OMC was famous for making only small changes to each engine and keeping the block and such the same across the board. Normally the tuners were different as well as carburation. Some years had different reeds as well. MERCURY was the one that made it complicated, they would make 6 different variations of a block and they would all be the same HP rating. You can always go here http://12.2.215.22/pub/default.asp?S...g=EN&brands=EJ and look up the different part numbers for each engine to see what changed.