I have a 97 ZX9 that I was thinking of swapping wheels from a 00 ZX12. Went to ronayers.com to check rotor and bearing differences. Theproblem I found was the rear bearings. I would just use the ZX12 rotor.
At denniskirk I found that the 94-97 & 00-03 ZX9 all take the same bearing from them.

ronayers has rearwheel bearings as
94-97 ZX9 601B6205 UG
00-03 ZX9 601B6205 UU
00-01 ZX12 601B6205 UU
denniskirk has all the ZX9's listed all for the same bearing. Does that mean I can use the ZX12 rims?

 

Here is an option for you to check out. If you get the OD measurement for the zx12 bearings and the ID measurement of the zx9 bearings you can usually go to an electrical motor shop and they can get you bearings to match your spec, typically much cheaper than you can buy bearings from anyone else. It still leaves you with seal problem though. Is the axle bigger on the 12? If so you could have your swing arm machined to accept the larger axle and just used the bearings and seals for the 12.

 

found out that the UU and UG don't change size.
But I am wondering if width bearing to bearing is different. That might cause the rotor or sprocket to be in a different spot.