If you are planning on new rims you may want to consider 16 inch .
The disc brake clearance problems aren't necessarily caused by the diameter, but by the contour of the center of the wheel as it transitions to the hoop. If it's got too wide a sweep, it will hit the caliper, while a sharper bend will go around the caliper. A stock 16" AD truck wheel won't fit without spacers. I tried a buddy's 15" artillery one day for grins and giggles and it doesn't fit either. The 15" six lug 72-91 (+/- a year) Blazer and 4x4 wheel is what is supposed to fit because it came on trucks with disc brakes from the factory. That's what the OP has pictured in the first post (four hubcap nubs, flat between the stud holes). Why one doesn't fit is still a mystery I guess, unless it's actually an aftermarket trailer wheel..?
Phak1, Some numbers for the 15" x 6" wheel are 14001279 and 560-00942, and there are several on eBay. I'm not having any luck with quickly finding numbers for the 15" x 8" wheels, and I don't have time to dig deeper because I'm at work...
One last note- when I was getting my parts in order to do the disc swap on my truck, I called one of the aftermarket wheel sources, maybe Wheel Vintiques? I gave them the measurements they asked for and they responded by saying I'd need at least a 17" wheel to fit. Clearly I did not, because I've been running these 15's for years. It's possible he meant all they offered that might fit would be a 17", but it was not stated that way.
