Truckstell made O/D units for Chevy cars from about 40-54. They were after-market items that Chevy dealers and other up-fitters installed in cars, and 1/2-ton pickups and Suburbans. There was a discussion about one on here about 2-3 months ago. They went in the torque-tube something like rfs56trk said. Try a search of these forums for truckstell. This is not the same as Ruckstell that made 2-speed rear axle conversions for Model T Fords.
