1953panel,
Can you post a photo of the mounting side of one of the lamp bodies?
I have original NOS lamps on my Suburban. However, the panel truck's rear-door "stops" are different from the suburban rear-door "stops". The panel stops allow the doors to open wider.
Nonetheless, I am surprised and disappointed to hear that the factory-style dual rear side-lamps hit the rear panel-doors. Let's see if we hear from other 47-55 panel-truck owners who have installed rear side lamps.