I heard that those lights were used on the center of the rear roof to offer illumination when a panel was making a delivery in an alley and the fully open doors would block the side lights. Leo (53 Panel) advised me to make sure the placement ensures the doors fully open without hitting the lights.
It's a small world, but I wouldn't want to paint it.
The bullet lights I purchased for my 1953 panel were actually from a 1938/1939 Oldsmomile. They looked identical except they were about an inch longer. They mated up perfectly and yes, be sure they don't interfere with the doors.