What motor is it

3=1973
M=Mound road assembly plant
318=engine size
R=secondary code for plant assembly use only
C=? this should be a number for the first digit of a 4 digit code for the 10,000 day calender.This positon should be a 3 to show 3802 as dec 25 1972 and its a saturday.
1496=the unit number built at that plant
The 10,000 day calender started 7/29/61=0001,it ended on 12/13/88=9999
Now this can change if the motor you have is a new type(magnum) casting,but I believe you have a older LA 318,mrmopartech