88 = 43mm.
89 conventionals = 46mm.
The 88 models' valving is OK, but the 89s' is better.
The 88 models use a funny "oil through the centre hole" style of shim, so I have no idea if you can buy alternative shims, and would need more brain power to revalve. With Gold Valves, they're excellent.
The 89 RWUs have a much more conventional "oil around the outside" shim stack, which should be much easier to revalve.
It goes without saying that the stock springs are ridiculously soft, and 99% of adults will need stiffer springs.
