Well, I think I'm just going to have to deal with it. Just by looking at it, it's obvious that the two threaded holes don't match up. The hole for the disc brake that I'm using is close(ish) to a match, but still lower than the opposite side. The rack seems straight, the frame seems straight, it's been working for a couple of months, sooo.... It leans, so be it. I'll probably be replacing that frame soon anyways, I guess that's just another thing to look out for.