With a Ric bridge, you are going to need to rout out underneath the bridge area as Ric bridges aren't flat underneath. It doesn't need to be pretty, as it will be covered by the bridge.
Taking 4-5mm off the top will mean you loose the binding, which will need to be re-done for it to look like a Ric. The neck will also stand quite proud of the body, which won't be like a real Ric, where the bottom of the rosewood on the fretboard is level with the body. The pickup cavities might also need to be routed deeper.