I just completed a refit on my T-3700 Hull #35 and found corrosion on the sail drive (another thread - another time) and made the decision to change out both the sail drive and the engine (rush of blood is the only reason I can think of).
This leaves me with a used Yanmar-3jh3e with only 1100 hrs on it for sale. It is currently in SouthDartmouth MA and I have it listed on Craigslist and would happily recommend it to anyone with a T-3700.
https://southcoast.craigslist.org/bpo/d/south-dartmouth-yanmar-3jh3e-40hp-sd50/7335089521.html
Will entertain any reasonable offer.
Best
Colin