I've had a few rides on my YSS and Wilbers fork springs this week. The shock was easy to install other than needing to grind a small amount of metal off the steel stamping in the frame where it mounts - it just barely fouled the shock body.
I haven't really had a chance to dial in the sag yet, just eyeballed it, but so far the ride on the freeway is every bit as nice as the stock shock (which was cushy and did not call attention to expansion joints), and the big lump in the on-ramp that I hit every morning leaned over at 70mph, which used to completely unsettle the chassis, has more or less disappeared from my consciousness. I like that. Haven't had a chance to take a ride on a bendy stretch yet, but I think there will be a big improvement.
The fork springs were super easy to install, they dispense with the silly plastic spacers that the stock springs use, they have slightly more preload than stock (my old springs were probably sagging) and there is far less dive on the brakes. The front end surging up and down during gear changes (even nice smooth ones) has been completely eliminated, and the bike feels a bit more planted up front, again without adding any noticeable roughness to the ride.
For my use, this is as good as it needs to get for the old K.