The only issue with running a SR500 rear wheel is sprocket size. About 39 teeth is as small as you can get. The hub portion of the wheel limits this. As long as ya dont mind shifting a lot and screaming rpm at 70, the swap is easy enough. I used the chain adjusters and bushings (the ones that go between the axle and swingarm) from a 80's yz, and the sr rear axle. This was on a drum brake SR mag.
I run a rd 400 rear 18 mag now...xs500 is the same I think. sprockets are available in smaller than stock XS sizes for reduced rpm on the hiway. Plus ya get disc brakes. I run a 130 90 rear tire.