Wish i could have helped more with this thouogh..
The stem should be 7/8". I had very recently tried to conform a Yamaha Vino stem to fit. With mods, it would work but i didn't choose to do any of the mod.(the vino uses a "real looking" stem/risers like a big bike) That mod has been on my list for either the S9 or the ZX. The naked bar look is sweet IMHO.
I would have had a link but my computer hard drive was wiped out recently and i lost a lot of information i had saved.