[Bill Pritchard]

P1P03C...

P = Muncie 4 speed, alum case
1 = 1971 model year
P = September assembly month (in this case, September 1970)
03 = day of assembly (9/3/1970)
C = M22

Is that 9976171 number cast or stamped? If it's a main case casting number, I have no idea what that's from, and it sure blows the P1P03C number out of the water.

Can't help you on the tag number.