In the late 60s and early 70s, I'd often visit car/truck junk yards. I recall seeing a few extinguisher mounts attached to the inner side-cowl on the passenger side (often next to a metal-box first aid kit). These would often be in school/service trucks that had no heaters.
Here is a
1954 GMC extinguisher and mounting bracket (on Rob English's website).
The extinguisher bracket/strap (mounting) was not sophisticated -
they looked like the least expensive of these.
