This is a common question asked and I thought we should start a new topic to answer these questions instead of hijacking another. It will be easy to search, use FAQ in body only.
The 1947/55 Chevrolet/GMC panel/suburban/canopy express all used the 1939 automobile tail light as a dealer installed turn signal option. Most were installed under the beltline, however some of the dealers installed them lower on the body in some cases.
The repros are close reproductions. They differ from the originals with minor details that only a purist would care about.
Reproduction lights are one light fits both sides, but the originals were designed to be either left or right only, you need both. The difference is no weep hole on the under side of the tail light allowing you do use the repro light on either side. Also, the rivet that holds the trim clip is in the bottom position on the original and one of the reproduction lights will have it on the top.
The chrome ring is a thinner material than on the originals, but the fit is the same.
All 1939 chevrolet tail lights were two filament lamps are
1154 lights Look this up under the 1939 Chevrolet section. The 1939 Chevrolet had only one pair of tail lights and they were used for both running lights and brake lights.
The only difference between the panel tail light and the 1939 tail light is the pig tail. The pig tail on the 1947/55 panel lights were much longer and has a different connector/plug. All of the lights used glass lenses and from my research, only plastic was available as a replacement lens after 1954/5. I believe that there was a major fire in the glass manufacturing plant somewhere around 1954.
This information was found on
TCLEDERMAN'S site and he has give me permission to post it here.
1947/55 PANEL/SUBURBAN SIGNAL/TAIL LIGHT TEMPLATE 1947/55 PANEL/SUBURBAN SIGNAL/TAIL LIGHT INSTALLATION INSTRUCTION SHEET. 
