MUSTANG RESTORATION help?
The engine appears to be a 302 with air conditioning. You are correct in that the details are rather vague but it appears to be a pretty straight vehicle from the pictures.
It looks like they spray painted everything in the engine compartment including the shock rubbers, the AC clutch, wiring, hoses, brake booster and everything else. The half vinyl roof doesn't appeal to me, but that's rather subjective - some else might love it.
I would never buy a vehicle from pictures and a description without carefully checking out the vehicle first hand, but $4000 seems very reasonable if the vehicle's running gear is in good condition. I suspect that if you are interested in this vehicle, if at all possible, you should check it out in person.