I would question the axle, steering box/pitman arm, and lift kit (if indeed present) istallations, as well as wheel type. Having disk brakes on the front generally is an indication that the axle is not original to the truck, most likely it's from a '73-'87. That shouldn't really cause any issues, should actually make clearance a bit better due to the wider axle. The steering box and pitman arm could be of concern, especilly if they were not properly clocked to center before installation. You should be able to get the same number of turns lock to clock. This could be componded by a lift, especially if the steering arm/pitman arm are not compensated for.
The tires shouldn't be an issue, as a 315/70/17 is just under a 35 x 12.50 in size. I've fit that size to known stock 63-'66 4x4 trucks without clearance issues. That leaves a potential wheel backspace problem that 46gmcpu mentions. There's a very likely possability that the po might have tried to use late model style wheels, which will cause all sorts of clearance problems.
