Had a false start with the wrong sized seat post clamp, but I ordered a new one and put it all together!
I'm really happy with it. I had to follow the advice of a lot of the reviewers on Amazon and reverse the seat post arms, but other than that it worked perfectly. I'm a little concerned with how I re-fastened the quick release axle. I put the springs on the outside of the rack arms and tightened it to somewhere that *seems* reasonable, but I don't remember how tight the clamp was when I started...
Now I have to order some panniers or something so I can actually use this! Might find some way to rig my backpack to the thing in the meantime...