You scored a great deal. Just my suggestion, but I would start with a leakdown test of the cylinders. This test would tell you if the issue is with the cylinders, head gasket, valves, etc. The most likely, top two issues, from what kills engines around here are lack of winter prep(cracked block), and overheating(head gasket or cracked head. Spend the effort on fixing the 140 and enjoy the boat. If you do the work yourself, you could make more than you have invested, and spend that on a V6 or V8 boat (preferably a Carlson). Too much to change to make it V6 or V8 from an I4. My $0.02, Plugcheck.