Need a favor from those with SBM and power steering.

Running w/o the second bracket could have caused enough vibration that over time that your pulley or PS pump shaft bent and is causing your pulley runout. If there is runout, then the belt tension is going to change as the PS pump rotates. There could be enough change that it's slipping intermittently as it's spinning and causing your grief.

One hint that this may be accurate is that belt tension changes the rpm range when it squeals. That tells me the amount of force/torque required at that rpm to spin the pump starts to overcome your belt tension. More tension is likely to aggravate the runout issue too. It sounds like you're going to need a good replacement pump and/or pulley and a decent belt along with your now complete bracket set.

Just my $.02 though. Hard to diagnose these kinds of things over the internet, but I can't imagine any amount of pulley runout helping your problem.