I would pull the cover and check the pullys' and belt for glazing (looks shiney and cooked)and alignment with a straight edge. If the pully is glazed but not worn (the V side walls of the pully should be straight)they can be sand blasted to get the glaze off, the belt must be replaced. Also, these engines are known for pully misalignment due to the mounting brackets and length of belt. See pic of how far mine was out of alignment! I ended up heating the brackets to bend back into shape. I have a higher amp alt that now runs without ruining belts every month. Am still thinking of installing an idler pully to help wrap the belt a bit more on the Alt pully.
Sorry about Picture size!
Alignment before (squealer)
Heating lower bracket to realign (on car)
Cooled and aligned
If the pully is glazed, hopefully it is just the Alt pully, I ended up blasting all of my pullys and powdercoating them.
Anyway, good luck and let us know what you found out.
Angelo