Honestly, I couldn't say exactly what did the trick. I maxed out every bolt just to the point they were almost all the way out and got it close enough that I was eventually able to muscle the belt into place.

The belts may be a little snugger than 1/2" deflection. I read 1/4" somewhere else so that's what I went with. The AC belt may be a little snugger than necessary right now, but I'll play with that again when it's time to use it. For now, I'm just glad the job is done.