Long term storage damage

Tyler, yes, the engine is installed and the seller (not the builder, who is, as I understand it, deceased) is plumbing new rubber fuel lines etc. in preparation for the sale.  To my (limited) knowledge, the seller (an A&P who may have known the builder, again my impression) does not intend to register the airplane or seek airworthiness certification, rather he is offering it for sale as is, expecting the buyer to register the plane and seek airworthiness certification. 

Well then, I guess the big question is: will "as is" be for an aircraft with an engine that actually runs, or not?

Aside from the big issue, of the engine not having run for years, there will be a lot more rubber needing replacement than just the fuel lines, obvs.

Here’s my long-term (7 months) storage issue:  
When “burping” the engine, a gurgling sound comes through the exhaust (in addition to the normal burping sound through the oil tank).  Last annual (November 2020) showed good compression on all cylinders, and it only takes 6 prop revolutions to burp the engine - so the piston rings do not seem to be the issue.  Would this be a stuck exhaust valve?  Any other thoughts?

Do a cold compression test and that will answer your question about a stuck open valve.