The price sounds pretty good going by how you describe the truck. I'm assuming the body is in fairly good shape and it hasn’t had a lot of bondo or shoddy body repair work done. Invest in a small magnet and carefully check out the rocker areas, wheel wells and such. Also look at the floor pans and cab supports from underneath the cab. Sometimes the firewall and roofs on these trucks will rot out if they've sat outside a long time.
Going by your name and profile, it sounds like you deal with restorations so this advice is probably obvious to you.
As far a mileage, 13-15 mpg is the BEST this thing's going to get - that is going downhill with a strong tail wind. I get 12 MPG on the highway with my 327/4 speed 1/2 ton truck. I'd guess 8-10 mpg in town, 12-13 mpg highway is more realistic.
Good Luck!
