I don't know if you checked out my schpeal on de-nivomatting an IRS... check the 700/900 FAQ on swedishbricks.net (I don't know if the brickboard one has the latest version). If you can get the car up on a lift (something I take for granted as every military post has an auto craft shop) and let the whole rear suspension hang free, the nivomat will be in an almost completely extended state. It sits in the control arm in an oval hole... if you can muscle it up about 1/2" or so you can twist the bottom of the shock 90 degrees and work it out of where it seats... I have done it this way numerous times and to the best of my knowledge the 88-91 IRS was identical with the exception of the swaybar added in '91 (heh heh heh). One other way to do it w/ a lift is to get the bolts out and use the car to compress it for you... I put a tranny stand under the bottom of the shock and lowered the car on the lift slightly so that it compressed the shock a little. Then I rotated it 90 degrees and raised the car back up... it fell right through that hole.
As for the springs, this is where things get tricky. I used two internal coil spring compressors, a large block of wood, two large crescent wrenches, and a 6' long iron prybar. Unless there's an easier way I don't know about, removing those springs is not finesse work. Quick and dirty, here's how I did it. After doing this about half a dozen times, you can get one out in under half an hour w/ the right tools and technique and a bit of luck.

a) PUT ON EYE PROTECTION AND GLOVES- spring compressors are very nasty. I am lucky to still have all ten fingers and two eyes after doing this whole procedure numerous times by trial and error.
1) Jack up car, remove wheel, shock, brake caliper.
2) put TWO internal spring compressors up inside the spring, clip them as far up as you can get them and let the bottoms hang out below the trailing arm.
3) while the suspension is fully extended, find something to wedge in there to keep the trailing arm extended as you compress the spring... otherwise, the already cramped space in which you are going to be working will become even more cramped.
4) take the two big crescent wrenches or other suitable crossmember material and lay them in the lower hooks of the spring compressor. This way, when you start to compress the spring compressor, they will end up up against the bottom of the control arm and it will pull the top of the spring down... the biggest problems w/ those compressors is running out of turns before you get the spring squashed small enough to remove.
5) work the spring partially out of its upper seat, now loosen the outboard spring compressor (the big long bolt will have gone up inside where the shock goes and prevented you from just sliding it out.... kind of a catch 22).
6) slide retension the outboard spring compressor w/ the big long bolt OUT of the shock tower this time... keep prying and working it further and further out.
7) same deal w/ the inboard spring compressor if you can't muscle the whole thing out by now.

Good luck, godspeed.

-Jon --
2LT Jonathan T. Belmont