| LEGO → System → Service Packs |
39 Motor Gearbox was a System Service Packs set released in 1977. It contained an OldGray 12 x 4 x 3 1/3 electric 4.5V/12V type II motor gearbox (Part x469bc).
External links
http://www.toysperiod.com/lego-set-reference/service-packs/lego-39-motor-gearbox/