Those LH threads are always super tough to undo. If you're repair doesn't work, I know where to find a replacement.
Belts are standard from a bearing shop. Kevlar ones by preference. Let me get back to,you on size numbers- I'll have to dig them up. Or just take the old one to them.
The idler pullies should move laterally about an 1/8" , I think. There is a step on the shaft that limits it. Reality is that if the belt alignment is good then it's probably not a big problem.
