dunno how to go about the spacer thing. I think the latter of your ideas, getting a maching shop to make it a hair bigger would be the best bet. As for the brake caliper, how is it mounted? the one on the xr has a bracket on it and a slot welded on the inside of the swingarm. They slide into each other tongue & groove style so it kinda holds itself up and is pretty difficult to bump out.

The "easy" way i found to do mine was just get the tire wedged in and centered with the axle holes. take a c clamp and push the brake piston back in to give you lots of room to get the disc wedged in. Put the spacers on the wheel and lift the wheel straight up to align it with the axle holes in the swingarm. You could prob use a small floor jack to lift it for you so you can concentrate on guiding the wheel up rather than trying to lift 40lbs straight up without knocking shit. naaaawwwww meeeeeeeeaaaan?

PS: NO ONE ELSE TOUCHES MY SHIT I'll do everything to my bike (except change the tires, but i bring them the wheel), including rebuilding it. If you have the tools and shop manual you can do ANYTHING.