When to buy an engine.

Calling on the group for advice. I have stumbled upon an O-320 off a C-172.
The engine has 2780 since new and is timed out. Although when ferried from
the south, on a 9 hour flight it only used 1 qt. I get the mags, engine,
logs and new carb for $4000. Is that good? No storage. It came right off
the C-172. I am only at the stage of welding up my fuselage but wanted to
know if this is a good deal and is it too early to buy my engine?

Ebby
Camden, NY