From what little I can find your looking at roughly 250.00 in parts and around 6 hours shop labor rate. So I’d figure roughly 800.00. That is if when it broke it didn’t damage a piston or valves. If it was running it’s highly likely piston could have hit a valve. I have no experience with them just doing some research. Maybe MbSeeks or Sliderman will see this and have some first hand knowledge. This is just my opinion but with what you have spent on that motor I’d seriously consider a new motor. But that’s all determined by your financial situation. If no other damage then chain might be a better option in short term.
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Charlie Weaver USN/ENC 1965-1979