use the GSXR axle
order 47x25x12 bearings from wherever
make a 68mm long X 25mm ID spacer for between the bearings from whatever material you want - I used .120 wall 1.25" OD steel tubing
can't remember the axle spacer dimensions - the gsxr axle has a step down on the left side so the left side spacer is shorter. if memory serves, that side is 12.5mm long X 25mm ID, and the right side is 25mm long X 25mm ID. I used .120 wall 6061 aluminum tubing for those.
if you search my posting history, I made a thread on it called something like "check my math" -- there's a simple spreadsheet calculator I linked in there, but it didn't account for the step down in the gsxr axle, but the right side is correct. work backwards from there.
brake rotor spacing is another story. also bear in mind that these numbers are for a stock XS hub - not sure if you're using that or a Harley hub with a 21" rim.