Well, to satisfy your curiosity, here's what my trusty AllData CD-ROM has to say. TSB 51907 dated Feb/94 covers '83-'91 700 series with Girling (Lucas) 2-piston front brake calipers.

It simply mentions that excessive wear between the caliper guide pins and their bores "might, in some cases" cause a rattling sound and that a guide pin replacement kit is available (P/N 271854-2) containing guide pins, bushings, dust seals and mounting bolts. Obviously this was not a totally uncommon problem for Volvo to have even bothered writing up the TSB.

As you and the others notes, a much more likely cause for front brake rattling noise is a broken anti-rattle spring on one of the brake pads. You can inspect these without removing the pads. If you're going to change the pads you should always pop the dust covers, clean and lubricate the caliper guide pins using high temp silicon grease. Use the same grease between the back of the pads, the stainless anti-rattle plates and the piston faces to help minimize any tendency for your brakes to squeal. If you've got ABS, now's also the time to clean up the tips of those sensors (check the 740 FAQ and archives for notes on this).

Once in a blue moon you should probably remove the caliper to check each guide pin in its bushing -mine wiggle a little and this is probably normal, but slop is not. This gives you a chance to properly clean and lube the guide recess. Shoot with spray brake cleaner and use a small round wire brush or something like a child's toothbrush (clean thoroughly before giving back to child). When removing a caliper, hang it up with a length of coat hanger wire to prevent damage to the brake lines.