I am looking at a Muncie trans for my 69 project car. The number on it is P3S29AC. Here is what I know about it:

P=Muncie

3=1973

S=November

29=29th day of November

A=???????

C=????????

What do the C and A indicate?

There is also another number stamped in the case up by the above cast number. That number is 23P33763.

The code after Muncie (P), the year (3), the month (S) and the the day of the month (29) - on a post 1968 Muncie indicates the ratio from the factory using an A, B or C.
I have no idea why there are both an 'A' and a 'C' on that trans ...
The other number stamped into the casting is the partial VIN identification for the original vehilce it was installed in - in this case a Pontiac (2), model year 1973 (3) assembled in the Pontiac, MI (P) final assembly plant - the last series of number seems to be missing a digit ...