Finally got the hardware to assemble the shoulder hubs. Gotta love Douglas Hardware! They have a whole aisle of bins of nuts and bolts in a bewildering assortment of sizes.
Note to self: Pay more attention when using the drill press. One of the hubs got stuck on the bit and it chewed the hell out of one side of the hole. That side snugs up to R2's body, so no one will see it.
Tried a test fit to the body and discovered that the body holes are a little snug. May be a good thing, though.