I have recently discovered that a 1957 plymouth uses the same springs as early B bodies and all the A bodies.
Front segment = 20" Rear segment = 35" Total length = 55" I ended up ordering a pair of Caltrac monoleaf springs for my '57. I told them I wanted a pair for a 1962 dodge with a one inch drop. The car sits exactly where it did with the pair of springs I ordered from espo springs, which I also requested with a 1" drop. http://www.springsnthings.com/