Not the braking I want

What is the MC if you don't mind? And is the rear pot going to the front brakes? I can't see from the pix if it has a prop valve with it already, but it almost looks like it. Got a close up pix?

OK, well, I would start with the bench bleed again anyway, sometimes those MC's play heck with getting all the air out. I only do it with the hoses that are open and dump the fluid back in and move the pedal slooooowly in and out.

OK, on the GM calipers. They have bigger pistons and so should result in even more front bias. So the fronts are definitely not working right.

If you have a brand and PN on the pads, let us know. Maybe the coefficient of friction can be found to see how good or bad they are.

The vibration squeal is usually eliminated with shims between the pads and calipers, or sometimes with a rubber-like glue like substance that you smear on the backs of the pads and let it setup a bit. The lube is for any pins and sliding surfaces.

You did clean off the rotors with brake cleaner? Make sure you get some brake cleaner and hose down the pads and calipers to get them cleaned. If the pads got contaminated (like if the rotors did not get fully cleaned), then it may be a challenge to get them properly clean.