just as an experiment i removed the rear disc from the final drive and this has reduced the offset by about 5mm, its down to about 14mm. i'm now thinking about getting a gs 1150 rear disc and wheel mounting it to see what the clearence is to the caliper. if anyones got and old knackered one, gissa shout!
i spoke to rory at GIA Spondon this afternoon and he confirm that there is plenty of material on the hub so milling 10mm off won't be an issue and he has sorted me out with an engineer that can do the work
heres some pictures with the disc removed
ming