Got the shell flush-cut.

I used a 1/2″ tall plywood frame, bolstered by 3/32″ balsa or basewood to yield an approximate .1″ lip once the frame is reinstalled. Putting a 1/2″ block yields a ~.35″ gap as seen. So the mid frame will need to be a tiny bit thicker.

The back got a little nick from some bit-chatter, hopefully that will putty up.