A 68 Cuda big-block fastback for $8500 - this is the best buy yet

I'd buy it.
$8500... Offer him $8000. Sell the seats, the wrong manifolds and everything in the last photo for a thousand or two. Now you're down to $6000. Looks like a New York, maybe a PA plate. Fender tag ?... Who needs it ?
You do realize the fenders and hood on it are fiberglass. I'd sell that **** along with the wrong seats and wrong manifolds and keep the steel hood and steel fender, and hunt for another steel fender for the other side.