a 15" wheel will bolt on to the dually 14 bolt without modification. I have it, another guy here, high5, pyro,(though pyro has since swapped in disks on the rear) it's been done lots.
the front calipers need to be ground to get 15" rims in them. some require a lot of grinding, some not much at all.. it depends on the rims you use and the backspacing they have.
rears yes. fronts no. you have to grind the calipers on the fronts to fit a 15" wheel. no big deal though as long as you have a chevy or dodge front 60. the fords used dual piston calipers that i don't think you can grind enough to fit 15" wheels though. i'm not sure about that though.
80 cj5 "high 5"
stretched to 100" wb