I just bought a '57 Chev 6500 with a 261 and 5 speed. I needed the transmission for my '57 5700 with a 265, as the SM-420 got cooked. All the literature I've found states there is no such thing as a 5 speed in 1957. It looks like it will bolt right in, the lengh is the same as the SM-420. Does anyone know what this 5 speed is? Any advice and/or identification would be most appreciated.