There are two routes to take for a firewall mount mc on an AD truck. The factory used a bracket that gave extra thickness to the firewall plus it extended to the lower bottom of the dash. This is the best set up if using manual brakes. If power brakes then there is much less pedal pressure to flex the firewall and an 1/8" plate on the inside of the firewall that runs from toe board angle on the bottom to pinch weld on the top is sufficient. Don't go thicker than 1/8 because the booster bracket bolts are pretty darn short. The one in the photo has the plate on the inside of the firewall.

[img]https://i.postimg.cc/tsfJ0HjF/S10-045.jpg[/img]

Evan