Hi Bill,
It took me a while but I finally remembered to measure this when I was home and type it in when I got to work.
The panel which came from Fran and which fits nicely into the recessed area of the vent is apprx 12 1/8" x 18".
Glad to see things will likely have a happy ending for you. I am looking forward to seeing your ride in paint.
I am back home now after a fantastic summer on the road and will be tearing back into my car this weekend (if a big package from RCR arrives). I can't wait!
All the best,