I'm trying to understand how the alignment works. The goal is the top left diagram, with the two pulleys aligned and the belt riding centered. What I have is the top right diagram, where the belt rides on the right of the back wheel's pulley and on the left of the drive pulley--and it squeals louder than my engine. I already have a thick washer as a shim inside the left frame arm to try to move the wheel pulley to the right. I hesitate to shim the drive pulley out from the frame because the driveshaft nut already has a reputation of loosening and I don't want to loose a thread.
I think most of the noise and wear is happening at the front pulley, so I want to get that centered. In both my examples A and B, I tighten the left adjusting screw and loosen the right adjusting screw. So both my examples should pull back on the left and let forward on the right.
So what happens?
Does A happen? Does it slide to the inside on the races of the pulleys where they move closer, like a rubber band sliding on angled spools?
Or does B happen? Does the belt stay rigid left-to-right and rotate with the larger flanged pulley, pushing the front of the belt to the outside of the drive pulley?

I would check the rear pulley to see if the pulley hub bearing is worn....if it is the belt tension will cause the rear pulley to run out of alignment with the rear wheel.  Grab the front and rear sides of the rear pulley (3 and 9 position on clock face), and see if you can rock it in and out.  If it wiggles....the single row rear bearing is worn.

In the old days we used to take a rubber carpet runner and cut shims, then DragBikeMike created a way to fix it properly with a double row ball bearing.

This is the proper way to get the pulley hub tracking straight.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1561964431

You can buy the modified spacer from Armen here:

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1641846528


I would also check your rear axle alignment by measuring from the swing arm pivot point on both sides....the marks for the axle alignment stamped into the back of the swing arm aren't always accurate.  A beam compass works great for this (if you have one).