I wouldn't put a gun rack in my pickup, because it advertises something to break in and steal. In the 70's, I dare say 100% of the pickups had only a single front seat, the gun rack in made sense. Today, probably >90% of pickups have a back seat and many of them also have a secure locker under the back seat. I also expect the average rifle costs at least 10x more today than back then, probably a lot more because of the accessories.
Now that you mention it, extended cabs were non existent and crew cabs were rare back then. Maybe they were from Leduc and Wetaskiwin.