Ok..so i have an old 1970 mercury 20hp short shaft that recently died and won't start, it has no spark in either cylinder. Not knowing too much about outboards I decided to just start looking for a different motor. I found one that's a 83 mercury 20hp but it's a long shaft...i was wondering if its even possible to swap lower units, and how hard it is to do so, or if I should keep looking for a short shaft. Thanks in advance for your help