The quality's there, but of course could vary, depending on what you find. The thing you really have to be careful of is to find a vintage Mustang whose pickups aren't overly noisy. This means that you really need to play and test out one before you put down money on it. I can't stress this enough. You might find a '65 Mustang, but it could be totally useless if it's all noisy (and you plan on keeping everything stock).
I got my '75 Mustang that had everything stock and original from a Guitar Center (gasp!) and they had '72 and '73 Mustangs that sounded like complete crap, but were priced higher due to the fact that they were older.
Oh one other thing: earlier Mustangs ('65-'68) are slab bodies, and later Mustangs ('69-'70's) have the belly cut, if that's something that matters to you.
Good luck with your hunt!
- Sean
