From Classic Boat Library
The following are manufacturers of sterndrive units. A sterndrive consists of a lower unit connected through the transom of the boat to an motor, typically a modified 4-cycle automobile-type engine. Some manufacturers such as OMC and West Bend offered their 2-cycle outboard motor blocks in sterndrive applications. Many inventors strove to develop and market reliable sterndrives with some finding success such as James R. Wynne with the Volvo Aquamatic.
The June 1961 issue of Popular Science lists a number of stern drive manufacturers past, present, and potential, including Eaton Powernaut, Volvo Aquamatic, Harnischfeger Sea Hawk, Sea Power Outdrive, Outboard Marine Stern-Drive, Mercury's MerCruiser, Brennan Motor's Imp, Muncie Gear Works' Flexidrive, U.S. Marine's Float-O-Matic, Brunswick Corp.'s Comboard, German-built Wido Commodore, Precision Gears and Product's Turbinautic, Kermath Screwball (introduced 1949). The September 1961 issue of Popular Mechanics and the June 1962 issue of Popular Science provides additional information on the wide variety of sterndrive units.
See the links below for more information: