Early in my career (1988) I actually drove one of those. It was a 1957 model p-400. It didnt even have reverse lights, and if you so much as touched the brake pedal on wet pavement or snow, the left rear tire would lock up. There was no fiberglass roof in the package compartment to let light in, just a pair of tiny glass "porthole" windows in the roof covered with screens. It didnt have a light in the back either, so if it was dark out you had to use a flashlight to see the packages. Low backed bench seat; lap belt only; high step; manual steering; 4 speed manual with a granny low 1st gear and an underpowered I-6 carbuerated engine; plywood shelves and BH door. You could not design a worse vehicle to deliver packages out of if you tried.
We called that car the brown coffin for good reason.
Drove one for 2 years 250+ miles a day.
Even on a dry washboard country road it wanted to swap ends.
Touch the brakes you never knew where the rear end would swing.
Learned to duck to keep from being scalped when entering the back of the car.
The brake pedal to the master cylinder was hinged with a grade 2 bolt, basically a shear pin and I had to find that out the hard way. It broke on a curve and there was a dirt path in front of me and I took it.
I replaced it with a grade 8 bolt on route.
Backing to the dock at UPS after a 280 mile day, I felt something wrong.
The rear axle holding bolts broke on the right side. when I was backing up.
The axle was cockeyed, by 10 inches.
If that would have happened on the highway?
Good/bad old days, glad we both survived them.