K7 shock eye to eye is 330mm

Sorry for the late reply. I just measured out my original SP shock, which measured 320mm eye to eye. I'm not sure if it makes much difference, but the pre-shock is wound up most of the way, probably 80% so that could account for some of length difference.
I don't see that making much difference, I think the fact that it doesn't collapse under my weight when I sit on it might have a greater effect!

EDIT: I alos noted that when I sit on the bike, it only compresses around the same amount as my '09 ER6F, so in I don't envisage the stiffness being a problem.

Adjusting the preload wont change the shock length, the preload is the amount of force applied to the spring static. You need to set your perload to give you a static sag of 5-10mm for the track and 15mm+ for road riding.

10mm difference shouldn't make too much difference should it?
Off to the workshop today so hopefully going to get it fitted up and take plenty of pictures!
Hopefully get some sort of guide written up for anyone else thinking of doing it!