the wheels are 15x12.5 with a whopping 6" of back spacing.

There is really nothing "whopping" about these wheels. Although, I would suspect they are actually 12" wide. I am sure someone out there makes a 12.5 just to make me look bad, but I am going to say that nobody makes a 12.5" rim. Most likely, he measured from outside to outside of the rim, not bead seat to bead seat.

6" of backspacking makes it a pretty neutral wheel. i.e. the mounting surface, is pretty much in the center of the wheel. Although, due to measuring I would bet it is actually a 5.75" bs, which is pretty darn common as far as wheels go.

Now, I agree with Sean. You do not want these, they will not fit. You really want a 15x8 in rim to run a 12.5" tire. You can do 10, but you might as well keep the bead where it is supposed to be when you air down. Wheels are cheap. You can get 15x8 rims, through Summit racing, in almost any BS you want for about $50/rim. If it is a custom BS, they will come unpainted, but so what?

I am running (on a pickup) 35x12.5s on 15x8 rims with 2.75" of backspacing. If I was to do it again, I would consider going to 2.5". I have the steering stops turned out a bit to keep the tires out of the frame and whatever other metal that was in the way has been removed. Troopers have a bit of different metal around the bumper/front body mount, but it is almost the same. Overall, I love this combo.

Michael