Here's what I decoded based on pictures 1-4.
1 - Casting Number: 591615 = 1948-54 SM318 3 speed main case - casting date code: D65 = April 6th, 1955 - No stamped serial number = indicates this was likely a service replacement (considering also the date cast was after the end of the 1954 model year. *
2 - Casting Number: 591615 = 1948-54 SM318 3 speed main case - casting date code D280 = April 28th, 1950 - Serial# HO113358 - HO = 1950 3100 series truck - 113358 = 112,358th transmission built at Muncie Plant (all Unit serial#s started at 1001). Serial# info taken from the
1950 Chevrolet Truck Data PDF.
More on the different main shafts in next reply.
* This makes your existing "original" SM318 not the original transmission from your truck, and of the 1953 and later design which requires parts specific to that design to rebuild/repair.
