Response from: Mark (Check me out!)

>>"this is the only one left, the other, a V-8 powered white convertible">"probably written off by GM, as often happens with prototypes and concepts. ">"4-speed automatic, unusual in the days of 3-speeders"<<
Not at GM: most of their autos from the late '40 thru the early '60s were 4-spd autos, the Powerglide 2-spd and the Dynaflow continuously variable units aside.

Response from: Philip (Check me out!)

Thanks for the comment, Mark. I'll stand by my remarks about automatics in the Banshee era as they weren't aimed specifically at GM, however you caused me to spend a little time with my classic cars mags in search of more info. It's true that the early GM autos were 4-speeders but by the late 50's 3-speeds were the norm except, as you mentioned, Powerglide and Dynaflow. Until 1961 a 4-speed Super Hydra-Matic transmission was available in some models but was then replaced by the new 3-speed Roto-Hydra-Matic. By the time the Banshee appeared, the 4-speed auto was history. Interestingly, 4-speed automatics are now old hat as automakers keep on adding gears.

Response from: Mark (Check me out!)

HydraMatic (1940-51), Dual-Range HydraMatic (1952-58) and Super HydaMatic (1959-64) were all 4-spd autos. The '58-59 Chevy TurboGlide and Buick FlightPitch/Triple Turbine could be classified as 3-spd autos, tho they did not progress thru all 3 ratios when put in 'D'. SuperHM (59-64) was used WITH the RotoHM ('61-64) depending on the model; one did not replace the other.
Of course, GM had a great number of models & powertrains, but this discussion can be boiled down to: GM was not WITHOUT a 4-spd automatic from 1940 thru 1964.
My earlier post got chopped up somehow: the white Banshee XP-833 convertible has been verified: it still exists happily in the Bortz Collection in IL.