Here’s a handy link to IH stamping codes, based on some information I found here:
N = 1968
P = 1969
R = 1970
S = 1971
T = 1972
W = 1973
X = 1974
Y = 1975
Z = 1976
A = 1977
B = 1978
C = 1979
D = 1980
I’m curious to see if the 345 in Peer Pressure dates the same as the frame, the body, or perhaps the VIN plate.