Look at this photo of a 1946 GMC. Notice the V Brace and the bracket at the firewall which your truck is lacking. It looks like each side has one of those bars.

https://www.barrett-jackson.com/Events/Event/Details/1946-GMC-1/2-TON-PICKUP-130321

Here's another 1946 GMC that has the same bar/bracket that the V Brace rods pass through and obviously keep it from sliding in and out of the firewall.

https://topclassiccarsforsale.com/chevrolet/82148-1946-gmc-truck.html

From close examination, of the photos, I'd hazard a guess that your brace is not correct for the vehicle. Your V brace lacks the bends just before entering the firewall.

Also, is that a PCV system on the engine in the picture below?
Attachments
1946 GMC Engine Bay.jpg (125.2 KB, 53 downloads)

Last edited by Otto Skorzeny; 08/06/2022 3:30 PM.
1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)