Well, the spacers didn't work. They simply moved the area of the rim that contacts the calipers. After a discussion with MCB, and their info from Baer, it appears Torque Thrust IIs are the worst wheel possible to have with big brake upgrades. Fortunately, they came with the truck (as opposed to me buying them), and while I like the style, they're pretty commonplace and I had intended to go with different wheels. I just hadn't planned on it so soon.
It sounds like I'll need to go the custom wheel route, and after much looking, I've landed on these:
I'm currently between jobs, but once I do I'll be ordering a set in 20x10 (front) and 20x12 (rear) after I ensure they'll fit.