Sounds like you are on the right track, only catch is, there doesn't seem to be anyone making 520 sprockets for a universal hub, or even weld on sprockets. If you look in X-birds Yerf upgrade thread, he milled down some 530 sprockets for his jackshafts down to the 520 size. Right now, that seems to be the only real option, other than finding 520 bike sprockets and cutting the middle of them out and welding them to a weld-a-hub, but then you risk making them out-of-round and having chain problems.
If have a look at surplus center's website, they have cheap weld on sprockets that attach to different sized hubs, I think that will be the way I go when I'm ready to put the axle in, which is soon, I hope.
