I did the GSXR shock upgrade on my B4 over the weekend.
Acquired a '92 GSXR 750 shock off of Ebay.
I measured the seat height before the swap at 30" from the lowest part of the seat to the ground. Then I placed the bike on it's center stand. Both the top and bottom bolts that hold the shock on the frame and linkage are 12mm hex and the nut is 14mm hex. The bottom one is easy to take out, but the top one requires a universal joint to get to the bolt behind the frame. You also need to move some cables and the air filter drain hose out of the way to get to the top bolt. I drifted the bolts out w/ a 1/4" wooden dowel and the stock shock just falls out the bottom. Getting the GSXR shock in is a bit tough since I didn't want to take off the air filter, overflow bottle, and battery box, but you can snake it up through the linkage and get the remote resevoir under the overflow bottle w/ a little prying and gentle tapping. Getting the shock in place also requiers a little gentle tapping. Then I lined up the bolt holes and pushed a wooden dowel through to keep them aligned. Then it was a simple matter to push the dowels out w/ the bolts and then tighten up the nuts w/ a little loctite. Hose clamps for the remote resevoir under the right grab rail and zip ties for the hose.
The seat height is still 30". Rebound and road feel are greatly improved. I still need to play w/ the adjustments more, but definately better than the mushy stock B4 rear shock.