I'm thinking of upgrading my v-brakes to disks. I know I need new hubs, levers, and calipers, but my question is whether my frame is compatible with disk brakes. I have a Gary Fisher Hoo Koo E Koo 2002. The Marchozzi EXR fork (also '02) has mounts that measure about 5 cm but the rear doesn't have this mount so I doubt the frame is disk brake compatible. But there are three holes (see picture below) and I don't know what these are for. Can someone please let me know what these three holes are four and whether they are for disk brakes? The distance between the two top holes is about 4.5 cm. Thanks!