ippytattoo
Just another grumpy old hack.
I just found a keihin cr special kit for the EX500 that logic dictates will work on the xs. http://www.power-barn.com/servlet/the-737/Kawasaki-EX500-Keihin-CR/Detail
Half the price of the awesome tm34-120's, http://www.mikuni-topham.de/ENGLISH.../XS650_TM34-B120_English/TM34-B120_XS650.html
I can't imagine they would run much worse.
My only questions would be fitting them into intake boots and supplied jets. It just so happened that the cvk's fit perfectly into the BS34 carb holders. The link you posted says they come with new spigots so that tells me that they do not fit in the original ex500 spigots and therefore not in the BS34 carb holders either. Before spending that kind of dough I would definitely be getting ahold of them to verify if they fit in the original ex500 spigots. Also since we are having to change the jets and needles on these a good bit their included jets may not be big enough for our application.