+1 manxman. You don't need to go all out to have the gains of the 21.
And after riding with the triple lamp I'd suggest any GS owner to get one. It helps that much.
No you don't need longer forks. The suspension travel stats the same. What you do is raise up all the mounting an hardware bits enough to give more clearance for the tire and muck. It clamps the tubes in the same spot and the ball joint geometry looks to not change. Just the spacing.
Did some dirt dirt trials today up and down and around some local construction. Very big a good change with the TKC's and the 21. Tomorrow is the real test. First set of TKC's and they are really nice - even on the road.
As your attorney, I advise you to buy a motorcycle. How else can we cover a thing like this righteously?