$6k would be better but he has probably $3k in a good motor rebuild. Perhaps shoot for $6k and max of $7500. Hopefully he has all of the original air cleaner etc.
There isn't a lot of detail in this ad. Color me stupid, but why would you rebuild a motor that only has 27k on it? i think he'll be owning that one for a while longer.
When I was growing up, this was the typical $125 car my Dad & uncles would buy as beaters. Gosh almighty have times changed! My first car was a '71 Fury 4-door. It was all a 17 year old could afford back then.