I am glad it's hooked up and "working". However, I think you were on the right track from the start about adjusting the main (bottom) pulley on the thrower. The main thing is to get the snowthrower's main pulley lined up directly below the tractor's PTO pulley so the belt runs straight (as straight as possible, within reason). From your first post, it sounds like you want the thrower's main (bottom) pulley to go farther forward (toward the thrower). That's good because from your photos, it looks like you have an inch or two of adjustment on the shaft to work with.
You can adjust the snowthrower's main (bottom) pulley by backing out the two (I believe there is two) setscrews on the shaft and moving it in or out as needed so that it lines up directly below the tractor's PTO pulley. Then, after the two big pulleys are lined up, you can slide the idler pulley in line with those two pulleys so that all 3 are lined up and the belt runs straight.
Note that you can take the snowthrower's main pulley off completely and turn it around instead of the way it is shown in your first photos, if you need more or less clearance one way or another. I recommend doing this if you can because this way, the setscrews are on the outside of the pulley and therefore are easier to get at for adjustments. FYI, I believe that you "could" also do the same with the idler bracket - if needed in rare cases.