There was a running change in the 3 speeds in late '56, that is what has caused the shift plate discrepency. You can just swap the plates to make it work. Also, on the '55-'56 trucks, the shift linkage is different from the '57-'59. There is a bellcrank on the bellhousing for 2-3, so the lever on the trans is inverted form the later ones and the passenger. You also have to use the truck levers with the truck linkage.
Also-technicly, there is no such thing as a "Muncie" trans before '63, and the true Muncies are 4 speeds, not 3. There is no differnce in the 3 speeds, only the assembly plant it different. It does seem that most of the ods were made at the Muncie plant. Besides, the od unit is actually a Borg-Warner, which was used on many other brands of vehicles and transmissions, even on fords.
