[rotorwrench]

There were a number of gear manufacturer's that made underdrive and overdrive auxiliary transmissions. They were made for any vehicle that might need them. Generally they were for trucks but they could be useful for other motor vehicles as well depending on necessity. Ruckstell, Warford, Muncie, and Brown Lipe just to name a few. As soon as any vehicle became popular, aftermarket companies jumped right in there to make accessories for them.