My belt has been sqealing lately. When I was looking at the belt I noticed
the alternator pulley sits back a 1/8in or more toward the motor. Which causes the belt to not be all the way on the pulley between the alternator and ac unit. I had the alternator off when I changed the plenum gasket.
Did I forget something or do something wrong when I reinstalled the alternator? And could this cause the belt to squeal?

 

I have seen shim's in the past that look like a small piece of pipe that shim the corresponding motor into the right spot. Further it could be that if it was a replacement that it could not have been pressed right from the manufacture. Please take a picture of it from all angles so we can have a good look and see what would be the best option to help you align it. It could be as simple as pulling the pulley back off just a tad.

 

I'll get some pictures it may take a couple days.