So is it a 270 or 370 engine? GMC used both or are you talking about the series of truck. If so it would be a 370 series would be a 2 1/2 ton. It uses the same cab as pickups unless it is a low cab forward model. These can be identified by a cutout in the door for the fender. Engines are interchangeable from 100 to 400 series without modifications. Front sheet metal.. hood, grille, fenders of all 300 series are interchangeable. I think a 400 series would be the same. A 450 series uses a totally different front end. If the front sheet metal is good, about the only expensive part to fix is the brakes and of course it takes 6 instead of 4 tires and they are more expensive than lighter tires.