It's tough to say. It's definitely not worth much more than $10k. I'd say $10k at most but thats just a guess.
Here's the thing, I daily drive a 71 Duster that looks pretty cherry. I could post a few pictures and make you guys think it's a show car. If you got an inspector out there to check it out, he'd have a laundry list of notations just like the ones above. A true 383 4 speed forumula S in very nice condition would go for a lot more than what you bid so it's not like you are crazy out of the ball park or anything. The good is he has a bazillion pictures posted of every angle possible. The bad is he fails to mention things like the sheet metal work and non numbers matching drivetrain. Plus the fact that the fender tag is missing really hurts the price because you now just have a nice car instead of a possible true rare vehicle.
It just depends on what you're looking for. If you want a car thats almost completely finished with little to no work left, then you can't be looking at 383 4 speed fastback Barracuda's if you only have $15k to spend. You can get a Duster or Demon thats basically finished for that much, but a Formula S is still going to need work at that price unless you just get really lucky.