From my understanding, the rear bumper was an after market accessory for the AD trucks and the license plate was designed by the Chevy engineers to hang below the single tail light on the left (as evidenced by period photos and the clear glass lens in the bottom of the tail light).
However anyone wants to place the tail light is entirely up to them, though.
As for me, I've had the rear license plate in the factory position for more than 20 years now with no issues.
Past success is not to be used as an indication of future success, however.
