If you offer $4k and he takes it he is not a savvy seller. #'s match , not too molested GTX , even in 67 [ later ones worth somewhat more] , if seller knows what he has and is in no rush to sell , can hold out for $10k and get it not to much problem.
I'd say Best look for another "money maker"
I'm assuming reasonable rust, and fairly complete, runs or will run.