I was able to use my stock one. I just welded a bung to the inside of the frame rails. It lines right up. Then the caliper rotates front or back to compensate for axle position from chain adjustment.
The only area where it's being a problem now, is that I'm now trying to figure out where to mount a fender brace/sissy bar - and the huge caliper is pretty much just "in the way", no matter what. So once I position a mounting point for the sissy bar, the caliper is not going to be able to move that much or it would hit the leg of the sissy bar.
I was thinking of cutting my stock one in half and taking a couple inches out. Then whittling down a threaded bung enough so I can shove it in one end and weld it in. Then put a piece of threaded rod in there. Then do the same thing with a bung on the other end, and turn the other side into it and use a nut (or 2) to make sure it stays in place. So it's "adjustable".
Anyway....the other thing I thought of doing was making 2-3 new ones out of beefy flat stock (like 3/16 in) and making the holes slightly different distances apart. So as I adjust the axle (which I don't foresee doing a whole lot) I would just swap in a stay with either wider apart spacing (if I move the axle back) or shorter spacing, if I were to remove a link, if the chain ever REALLY stretched.