Unless you know how to do metal work I'd walk away from this car. If it was just the spare tire well or a floor maybe, but when the rocker is rusting out on the top, that means the bottom is gone.
If your heart is set on this one, talk him way down. It's advertised as a 340, but it's a 318. Might be a worth $2500, to me I'd pay that, but not a penny more for it.
Your in Texas, lots of decent cars down there.
Riddler