Hi bubbagates,
Had thought about the same idea. A 1/4" mount oversized, then use standoffs to the firewall so you can still adjust the thrust if needed.
Did you glue or laminate the plywood with a carbon sheeting ?? kinda looks like that ??
If you can at your convenience, like to see any other pic's you have. I'm abit challenged in this area of custom mounting.
Thanks alot. Dan