See you have a double belted AC car there, double belt on the Alternator too. Make sure these 2 components are not part of the problem and their belts. Alt pullies can squeal, AC clutches can Squeal, AC pumps can start going bad turning hard, 2 old belts to squeal trying to turn 50 year old parts and worn pullies.
Get it all checked out to make sure all components are good, free rolling bearings.
All back together, start it up at a fast idle. Turn the steering wheel to full lock to the right and hold it there. That puts a good load on the PS Pump and wiil make a belt squeal if things are not right.
