I'd ask about how many hours are on the 'rebuilt' top end.
Some real riding time means it's alright, someone saying and hour or two makes me wonder what went wrong for them to park it. Receipts are good too. Some people's top end rebuild consist of a cheap hone, new rings on a used piston, and generic name gaskets.
$1,600 can turn into $3,000 real quick if you have to replace or rebuild much.
How it's stored says something too. In a barn or shed without a cover, they didn't care too much about it. In a shop or garage with a concrete floor is better.
I professionally repaint everything with Rust-Oleum.
The story of three wheels and a man...