I completely gutted my 71, and most of a 75. Never saw anything quite like that, but it's close to a package try support.
The first picture is the support that goes under the lower dash section to connect to the A pillar. 2 required and they are right and left, not interchangeable. They go in after upper dash is installed, when you bolt up lower dash (tray up to 72, then the glovebox 73+) The second bracket goes behind the instrument cluster and connects the firewall to the brake pedal support bracket. It goes in before the dashboard.
Thanks everyone. The pictures from Mavman72 made it clear what I forgot to do. Easy fix this time, not as usual!