Should I save this 1984 Volvo 760 which has been sitting since 1997?

[Goteborg Vapenfabrik]

Sorry for this bad news. You have a bent valve or multiple bent valves. Any engine for sale on fb is just as likely to be damaged or worn out. This type of damage does not require cylinder head resurfacing, the cylinder head may be salvageable, you need special expertise here, not just someone looking to profit from your misfortune. Tom Bryant in Maine is your safest option, if not the most expedient one.