For what it's worth, I am also working on the clutch mods recommended by Turk for my 2001 SX700R. I was given a part # (90201-45592) for the shims off this site which unfortunately turned out to be the wrong size. The inside diameter of the shims was about 5 mm too small and the shims will not fit in my clutch cover. If you happen to find a different part# for the shims that work for you please let me know. I may decide to purchase them. Although I don't believe the shims will do much other than raise the engagement rpms a little. No speed gains from what I can figure. I'm sure someone will correct me if I'm wrong.
And a little side note, I installed my new 51/43 helix and added the recommended rivets to my clutch weights and rode it yesterday with just those mods. I'd say it was a noticable difference and the sled seemed to pull a lot harder. Top speed is about the same. I'm still waiting on my new 14.5 rollers and I'm not sure what they are going to add to the performance. At $25 per roller I'm tempted to return them and just ride it with the new mods I've already done. Oh, and the new rivets in my weights brought the peak RPM's right to the desired 8500 rpm range. No over reving anymore...
I'm going to pass on doing the head gasket mod for now. It might add a little extra power, but fuel economy may suffer and with the added risk of failure I just don't think it's worth it. Although having never done it before, I don't really know if it's worth it or not.

If you do the mod, feel free to post an update of what you think. I'd be real curious...
Good luck with you mods and enjoy your sled!