Truckstell made a similar setup for Ford- - - -as far back as the 1920's. I had a friend with a Model TT fire truck with a Truckstell system, but I believe it was an "underdrive" that allowed the driver to select a very low ratio starting gear to get the rig moving. Since the T model only had two speeds, the ability to gear down in both first and direct drive allowed coach builders to exceed the designed gross weight for commercial vehicles.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!