Many thanks to REBinc who helped me figure out how to do this. It's not perfect since I overestimated the acuracy my dremel tool could cut with a fine cutter. So I've got a ragged edge at the top. This will probably nag at me until I decide to just go and buy another frame and re-do it. For now it's alright.
For anyone doing cutting on plastic, the fine cutter is precise enough but it can't sling melted plastic away from the cut fast enough so you end up with globs of dried plastic on the outside of your cutting surface. In hind sight I should have cut inside more and used a rasp to shape the edge. The rasp helped a lot but there was still too much damage to completely clean it up.
I also included a shot of SHEILA's cockpit as it stands right now. I got the ZR3 remote warning light installed which was a big help since the head unit is not out of my line of sight.
No matter what it's really nice to have that display built in now. Very nice ;-)