stick a thin piece of wood in both sides of the rotor if you hit the pedal with the pads out. I am pretty sure the rear calipers will psuh both pistons out and blow fluid everywhere without oads. I would have two new calipers in hand once I committed to opening the brake system, if it is that locked...

Also replace any flexi brake hoses at the rear.

Neil.

In all of my Volvo owning years in areas where the roads are salted, the rears have usually failed before the fronts by seizing.

Good Luck!

Neil.

I have had OK luck (about 18 months so far with no issues noted) with NAPA Adaptive One calipers on the rear of my car.
There is a helpful write-up on brake caliper issues/repairs here: viewtopic.php?t=102449

They look like a good reman unit. I like Nugeon as up here they are cheaper but well coated in their higher quality option. Napa stuff up here is getting really silly priced for some reason.

Neil.

I think I would seriously clean that metal and just epoxy the bump stop back on

I think I did come across this once. I mount them up using whatever bolts I had. The clamp force at proper torque won’t be impacted by an extra mm of bolt hole size

Unmetered air will mess up your idle , and if it runs well at revs, that also points to unmetered air.

It’s a drag, but you have to remove an inspect each vacuum hose on the engine, including the hidden ones. If they are 28 years old, they are past their ptime

I picked up a smoke machine for well under a $100 ( Autool SDT 60 - made in China, but REALLY well made ).
Kind of invaluable when working on these old rigs with old hoses.

30 seconds of propane heat on those flare nuts amd off they come