Kahler cam trems require a 2" wide x 2" long x 0.5" deep route for the cam block.
If you want to put one on a guitar that has a recessed Floyd type route, it will have to be filled in (at least on top) so the bridge will have something to sit on top of.
If the guitar has a non-recessed Floyd, you don't have to fill anything in but:
1) You will still have to route out the top of the guitar to accommodate the cam block.
2) There will be small hole on either side of the Kahler's baseplate from the original
Floyd trem route (unless you fill them in of course).