Nice worktruck. I just to build models like that. From the looks of it, it has the 7.3L diesel. Just the EFI badge under the left headlight is misleading, as the diesel has a mechanical injector.

actually it has the 460 Cube gas burner, it's fundamentally the same kit as the Revelle F-350 Dually, only difference is it's missing the dually tires and fender bubbles, and the badge work is changed to F-250. also the 7.3L International Diesel V-8, if my memory serves me, was made after 1989, in the '80s the diesel was the 6.9L International V-8. now I may be wrong. but hey, the exhaust stack, 5th wheel, rims, tires, emergency lights, and grill guard are all custom parts, the grill guard was a custom made part.