im using ISR radial with intergrated Resivor. it dosnet have a great capacity but works well i think it was a 17.5mm bore but best thing to do is call this guy he'll tell you exactly what size you need.

http://www.p3unlimited.com/master_cylinders_front.htm#radial

here is a pic of mine before i change the clipons so i could tunr the bike LOL oh yeah and then i needed new throttle cable's as originals are to short with new clipons. Im still getting use to the feel of the new brake but hand on heart i thought the original unit was better than this. Maybe im just not used to the feel yet!

http://www.bikepics.com/pictures/530306/