For the Girling (Lucas) Type I dual piston calipers used in 1989, guide pin and guide pin bushing wear can cause brake rattling. Volvo documented this in TSB 51907. Volvo has a kit p/n 271854-2 which includes guide pins with integral bushings, dust seals and mounting bolts. FCP Groton can order it in for you. You'd have to ask them if the parts can be ordered separately. I wouldn't think it was worth the effort or the safety risk of a seized caliper to machine your own. You'll have enough entertainment pressing the bushings out and back in. BTW The bushings would be steel. Note that the upper/lower guide pins are slightly different (kit has colour coded pins) and the order is different side to side (left upper is black pin, lower is yellow; right upper is yellow, lower is black). Make sure you thoroughly clean out the guide pin bores and re-pack fully with high temp silicone brake grease (should come with the kit). Everything should be torqued to spec: Guide pin bolts 22 ft-lbs. Caliper bolts 77 ft-lbs. Lug nuts 66 ft-lbs.

While you're at it, check the rotors for runout and thickness. Apart from pulsing, a warped rotor might aggravate caliper rattling. The minimum thickness will be stamped on the back of the rotor (ventillated rotor should be something like .788", a non-ventillated would be .433"). The runout (at approx 5/8" from the outer edge) is .003" max. If the runout is less than about .007" then you may be able to reduce it by shimming the back side with unwrinkled foil sheets around at least two studs. I don't see a spec for disk thickness variability, but certainly it should not be more than .0012" max. Resurfacing (turning) a worn rotor isn't worth it.

Hope that info helps you