I have a 52 gmc ambulance. If you look inside the door behind the light you should find a steel reinforcing plate, has holes matching the light studs. Seams I read somewhere that those lights were supposed to be able to be used as steps. Don't know if that's correct but the stainless trim on the top would protect the paint and strengthen the housing. Just a thought... my ambulance had the OEM taillights on both doors.
Happy New Year
Richard