Another question: Do the dually rims for these pickups allow to run 255/85 R16 tires? Who has run them?
Has anyone ran these 10 lug adapters to use 19.5 rims off a newer F550?
http://www.arrowcraft.com/index.php
People will run all sorts of stupid-sized monsters on dually wheels. Just cause it doesn't roll off the bead doesn't make it a good match. IMHO the widest a factory dually wheel can fit properly is the 235/85-16. However, be aware of the wheels offset - 2wd dually wheels are made for 215-wide tires, if you give them some aggressive 235s you may very well find that the sidewalls are now touching. Not always an issue, but it does happen. Ideal solution is to locate a set of proper factory-4x4 dually wheels, they have a bit more offset built into them and thus can fit 235s in all sorts of nasty-looking tread designs. Don't need a full set of 6 there, just 4 will do the rear axle nicely, front can run 2wd wheels no problem, just remember not to rotate wheels front-to back, just side to side,
Regarding the 19.5s, forget adapters, IMHO that's a lousy way of going about it. Look for 19.5" wheels off a P30 GM chassis instead, that would be your typical older Frito Lays type box van - those have the proper 8 on 6.5" bolt pattern, you'll just have to have the center hole (hub pilot) opened up to 4.88" to slide onto the Ford hubs. Same trick actually applies to the 10-lug F-Superduties too, only there you use the wheels off a 3500HD GM truck. Keep in mind the 8-lug P30 wheels are not super-easy to find, may take a while to locate a full set of 6.
Oh yeah, 19.5" commercial tires ride quite rough and can't air down well, may wanna think about that depending on how you plan to use the truck.