Rebuild or Purchase

[jboyle1650]

I have a 1977 365 Ketch with a Westerbeke W40, serial number 108U84698B607.  I've pulled the engine to have it rebuilt.  I live in Austin TX so skilled sailboat mechanics are in short supply.  I'm being told the engine rebuild won't happen until the end of the year and I can't get an estimate until they pull it apart.  I have found an engine on eBay that was rebuilt in 2010 it has 350 original hours and 93 since the rebuild.  I can get it plus the transmission for $5500 with shipping.  I would like to take this route since it will be quicker but have a few questions.
How do I tell if the engine is compatible?  It says it is a W40 with a paragon trans which is what I have.  I've asked the yard what the serial number of the engine is and what it came out of but haven't gotten a response.  Looking for some advice on how to proceed.  eBay offers a buyer protection plan so I believe, although, I've yet to thoroughly research what that means but will if I proceed.  Would you rebuild or buy.  The yard that has my engine is a Westerbeke certified dealer.

[SVJourney]

If that is for real, you could sell a low hour Paragon for half of what they are asking.  Plus you would get many spare parts out of the deal as well.  Crap shoot for sure though.