The correct move is to put a wheel from FZR400RR which is identical to the FZS600
So you have tried it? Great!
Does the speedo fit spot on?
Bearings, axle? Can I use them from FZS, or I have to get FZR400 axle and bearings?
160 rear is common, but 110 is a bit harder to find, so I'd look for front wheel swap.