Squealing belts usually indicate a missalignment of one or more pullys. I would use a long rod and while idleing put the rod on each belt driven item to make sure it wasn't a bearing going south.
The most common squeal on that engine would be one of the idler pullys. Them things have rollerskate bearings in them and are known to be the weak link in the single belt systems. Take the belt off and examine them for wobble or possible FELT grinding in the bearing. If there is over 80,000 miles on the idlers I'd just replace them anyway.
Big Jim

professional bovine relocation specialist