The previous models were injury/death traps.
Spending an extra hundred bucks per vehicle for a nice N-way adjustable seat or spending engineering hours making the seat-belts more convenient will have far greater benefits than throwing random safety technologies at it.
The previous models were designed in the 1980s. All 1980s work vehicles are/were death traps by modern clipboard warrior standards.
That speed is quite deadly with zero crumple zone.
If you're not wearing a seat belt then you're going through the windshield and it doesn't matter how the vehicle is equipped.
A crumple zone is going to still help in that case (40mph head on with another car at 40mph is significant, crumple zones in both vehicles would help both occupants).
Can't they just write "DO NOT BEND" in sharpie on the side?
Particularly since they routinely swing in and out of the roadway without looking or even using their directional signals.
It's best to treat a mail truck on a roadway as a being of pure chaos, utterly unpredictable and capricious, if not always actively malicious.