The thing about Suzuki is they often use the same yoke spindle sizes, so for curvys the pre-SRAD era GSXR slot straight in. For pointies it's the Y2K GSXR. I suspect it could be the same with your gladys, but as a GSXR 600 K8 rear shock is the cheapest rear upgrade, from what I read in Performance bikes, maybe a late set of forks from similar age GSXR?
Have you looked over on svrider to see what the yanks have done?
http://www.svrider.com/forum/showthread.php?t=114250