Having been an engineer for some years and a 750 Honda owner, I guess the only real way you can find out is by measurement ! The diameter of the bearings, if you use tapered the outside diameter of the race may be too large for the 750 frame, but (possibly unlikely !) a hardened sleeve could be made to take up any difference should the Ninja fork race be smaller. I would think if the spindle is too long, once the yolks are on another machined spacer could be employed to take out the excess length of the spindle. Another possible way would be to have the spindle removed from the bottom yolk and replaced with one to the same spec as a 750 Honda !
I like the idea of what you want to do - may look a bit odd but should work, Good luck !
Gouldie.
