Woo! Score man. It looks boss.
I did this mod to my iBook G4 a couple months back.
I put a small piece of cut/bent aluminum over the gap in the optical bay.
And I was brainstorming.. You know how MCE has the Superdrive thats designed for the tray loader slot in the G3?
I wonder if that would fit correctly, and fill the gap nicely. I'm not sure the mount points would be the same, but most optical drives follow a slim-line standard. It would be worth a try, I think.
I left mine clear though, and LED'd the bottom (off the 5v from the Firewire :D)