Originally Posted by AutoGear
Well its not a Muncie; since its cast iron. That leaves you with a T10 or a Saginaw, most likely a saginaw. If the reverse lever is in the main case, its a saginaw, if reverse is in the tailhousing, its a T10. As to whats inside the castings, you can never know for absolute certain unless you count the teeth after you open up the sidecover.
Or it leaves him with a NP420, NP435, A833, or some other truck transmission.