#GM3952648 located on the 7 boltsid plate
#3885010 located on the side case
2 rings on the input shaft
Patent #3088336
P1206
Speedo on pass side
Thanks Bill

Does not compute :confused:

2 grooves on input shaft = M20.
3885010 main case is 66 or 67.
3952648 side cover is 70 & up.
P = Muncie 4 speed.
1 = 1971 model year.
2 = ???? This digit should be a letter defining month of production
06 = 6th day of the month.

1966 and earlier used a different date code format. P1206:
P = Muncie
12 = December (1965)
06 = sixth day
The case, at least, is a 1966 model year case based on the 010 casting number and this date code.

The entire transmission may be a 1966 M20 with the exception of the side cover. An original 66 side cover would have casting number 3884685 on it.

Go along with Bruce here, 63-66 used Pmmdd, 67-68 got year number and letter for month like P8A01 (1968, January 01), and 69 through 74 added letter for M20(A)/M21(B)/M22(C) like P2R25B (1972, October 25, M21)

Early Muncies (64-68) used a stud on the side cover for the shift levers (secured by a nut) while later used a bolt through the lever into the side plate.

I guess if I had looked in the correct year section of my 'Chevrolet by the Numbers' book I would have seen that graemlins/clonk.gif

Thanks Bruce and Dale for catching my faux pas graemlins/waving.gif

Thanks guys, it looks like the side cover got changed.

Thanks again, Bill