1967 Mustang, should I buy?
It wont be a V6.
Its either a straight six cylinder, or a V8, probably a 289.
Either motor is reliable, and cheap and easy to fix. The automatics are a simple box and cheap enough to replace and repair also.
If there is no major rust, and you can live with the bad paint, it would be a ok car to drive around, if you dont mind no power steer, and no air con.
$4500 is probably a bit rich, maybe offer a bit less. A paintjob will cost you between $1000 - $2000 so keep that in mind.