The sheet stock idea you mentioned was what I had in mind. I was thinking of possibly a small electronics box (like from radio shack) to hold the display with sheet stock cover (lid). The other thing about an oversized plate is kinda like the gauge panels you can get through speedway motors, just a plate with a sized hole (or rectangle) for your gauge to slide into and rivet to the dash. The screws would have to hold the gauge to the plate instead of your threads. If you have access to a cnc and the threads aren't a money issue, then by all means go with that. It looks great the way you have it. I just figured any reduction of machining would save you cost and open up some other possibilities for housing shapes.
My only concern is if you sell too many, when does INEX say its a non-as deliverd part that gives onboard data acquisition?
You got a great product as is. Keep up the good work.