Ok, so after putting it all together, even with washers, the sheave and belt both rub on the frame. I went ahead and dimpled the frame, but now, after getting it back together, it turns out that I must not have supported the frame well enough while doing it. Looking at the bike straight on, the fork is leaning to the left. I sighted down the frame, and it now has a long twist along the length of it.
So, it looks like I have to dismantle it completely, and try to work it back into position. Yes, there is no joy in Mudville today.