I got the main rear subframe bushings in (the 4 big ones) and loosely installed the rear diff mount. These delrin bushing fit perfectly, just a bit of grease and some love taps from my rubber mallet and they went right in.
Unfortunately I then realized I has completely forgotten about the small crossmember and went and dug it out from under the car. Unfortunately it's in much worse shape than everything else, so I'm going to get it sandblasted.
I ended up snapping one of the studs on the weight/block of metal that bolts to the crossmember, does anyone know what this thing is actually for? It's part #51277‑20010 and it looks to be some kind of counterweight, if I need it I'll drill out the stud and put in a bolt, but if it's useless I won't bother putting it back in.