Thanks...it is. The measurements I had gotten from another blank-out plate were 8 3/8" and yours seems just a wee bit shorter. I made the mold for 8 3/8".
As for attaching it to the dashboard, there are two options. Which one I choose depends on how the speaker plate can be mounted. It would be really nice if GM had put some screws up there somewhere but they didn't.
Thanks again.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end