There were no standard equipment dual tail lights during Advance-Design years (1947-1955).
It looks like RPO 249 (Regular Production Option - factory installed option) dual tail lamps were available from 1950 onwards only on/for Advance-Design panel-body trucks.
It looks like accessory (dealer or customer installed) GM dual-filament right-hand tail/stop lamps were available all Advance-Design years (this most likely matched the stock left-hand tail/stop lamp).
Accessory (dealer or customer installed) truck directional signals kits were available from at least 1949-1955st. However, through 1953, the dual rear signal lamps were in addition to the different-shaped single tail/stop lamp.
