Hmmm....
Well, although it's been mentioned briefly on the old site before, I thought the following would do the job.
YZF600 thundercat forks - they are also 41mm, but 40-50mm longer than the FZS600 ones. To compensate, fit
VFR750 clip ons or similar as they are more 'raised' than the usual sets, and so might not foul the tank. A customisable set of clip-ons would definately clear the tank, but of course would cost £££££££
I'm thinking - take off the standard bar risers. The clip-ons would clamp on to the excess fork length and still give a near standard ride height.
The mudguard would probably require a bit of messing around with some spacers.
Bikes weight the same, so heavier springs not needed.
The only real concern would possibly be the extra fork travel of the YZF forks - but not sure how much travel they have.
So you would then have preload, compression and rebound for the front-end.
Of course, this would all be theoretical, and is likely to stay that way since I no longer have the 600.....however, someone else may think it's do-able & take up the challenge?