Nice score on the 1987 and welcome to the world of Marshall
I've got one of those 1987XL's, and yes it's loud as hell!!
I ended up putting a LAR/MAR master vol in one of the speaker jack holes, and it's much more usable.
I've had a Rivera Rockcrusher recording here for a while, and I like the sound of the master vol better vs the Rockcrusher at band volume. Neither the Rockcrusher or the Lar/Mar sound any good at bedroom vol though.
Haven't tried any other attenuators other than the Rivera unit.
Keep in mind that the XL re-issues are closer to a 70's metal panel spec than a late 60's Plexi spec. so all 3 filter caps on the reissue are 50x50uf. If you want to get a little "browner", change the preamp filter to 32x32uf and the screen filter to 16x16uf. Leave the mains @ 50x50uf.
There's also no bypass cap on V2a on the reissue, so you can add a .680uf there if you want a little more gain.
Finally, as the Lar/Mar master is inserted into the negative feedback loop, sometimes it's beneficial to lower the NFB resistor from 100k to 47k to keep the same feel. Alternatively, just moving the purple NFB wire from the 8ohm tap to the 16ohm tap would be like lowering the NFB resistor from 100k to approx 68k. That may be all you need.