Okay... scratch that.... I'll post my "shock" reply here:
Spring to replace the Progressive 420 Brick: Hyperco says they have a 6" free length spring, in weights of 350, 450, 500, 500, 550, and 600+. $81 through performanceshock.com . Problem is that the stock B12 spring is, like, 6.75" in length... so not sure yet if it will fit. Also, my Prog. 420 spring says "400-450 lbs" on it... so not sure what the Hyperco should be.
Pesnke makes two shocks that would fit: a "sport" shock with NO reservoir and NO compression damping adjustment: $575
Penske 8983 shock, with reservoir and full adjustments: $769
Ohlins... available, buit prices range from $900 to $1100. Too rich for my blood, although I love that yellow spring.
Older GSXR / Hyabusa shocks: I tried a 1992 (?) GSXR 750 shock before; it was okay, but was longer than stock and altered my steering... gave me an odd, low-frequency front-end shimmy, especially on the highway. Be careful: some shocks that actually fit are quite longer than stock; be prepared for substantial changes in handling... including possibly making your front end more twitchy or unstablee.
I'm also interested in info regarding GSXR fronont-end swaps for the B12. Anyone got experience with this?