I've lost track of who has steel wheels and who is still looking. But for the record, I've been through the wheel problem. I have used 16" Ford steels with shallow enough back-spacing, 0" offset 7" Ultra alloy wheels (no longer made), 8" American alloy Ford-spec wheels and finally 0" offset, 6" wide 10-hole, alloy, trailer wheels with 8-hole mounting from Etrailer Supply. All the combos I've mentioned are 16."
8-inch wheels with the right backspacing to clear the tie rod ends will put the wheel/tire combo centerline so far outboard of the kingpin centerline that the truck becomes very hard to steer in a straight line. It will follow every pavement aberration and is very difficult to control in pavement ruts at over 40MPH. It's worse loaded. I know this from experience and it's not safe.
The factory setup was "centerpoint" steering with the wheel/tire centered on the king pin axis. This had two benefits: easier steering at slow speeds like parking and more controllable on the rough roads for which the trucks were built. The original wheel offset was about 9/16" Inboard of the centerline on the 5"" wheels. 0" makes for acceptable handling with 6" wheels but as the wheel gets wider the centerline moves outboard by half the distance of the increase. Wide tires makes the situation that much worse.
I hope this helps someone who hasn't already spent heavily on 8-hole wheels
