Otto: The '56 GMC HydraMatic transmission (and up thru '60 at least, I think '62 but I don't have documentation) is the same design as used in '40 through '54 Cadillac transmissions. The Dual-Coupling HydraMatic in your '56 was first used in '55 Cadillac until it was replaced by the Turbo Hydramatic 400 in most Caddies in 1964.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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