I thought the F450-550 trucks had 8 lug rims. Have to look closer next time I see one. Or are you talking about the old F450 that was coined F-Superduty? I'd like to get one of them to trransplant my engine into- 14" rear disc brakes, and heavier front suspension. Oo. Either way, I'd see about getting a set of wheels from Rickson, et al, and seeing if they can make a set for our trucks. 2nd Gen (16 or 19. 5) rims wont work on our hubs; ours are coin fit, the later ones arent. As for tires, I'd see what kind of deal i could get at a local shop that sells retreads.
Daniel