There is a lot of confusion out there about what is a Muncie and what is a Saginaw. The Shop that I buy my 55-67 3 speed parts from calls that transmission a Muncie. It is Anaheim Gear in Anaheim, CA. They have probably built more of these gear boxes than we will ever see in a lifetime.
With regard to other 3 speeds in later vehicles, I am looking at page 7M-14/15 of the 1974 Chevrolet Passenger Car Service Manual which states: "Note: The 3-speed Muncie unit is similar to the 3-speed Saginaw design but differs in that it has a 3-1/4 inch center distance between the mainshaft and countershaft instead of 3 inches, and has larger bearings, gears, input shaft, and mainshaft. Power flow is essentially the same for both the Saginaw and Muncie transmissions" Also fig. 15-Muncie 3 speed - Transmission cross section.
I don't imagine this lessens the confusion any. Fred
