Bryant Age

I’m stumped but I think this unit is maybe as old as 1968. Can anyone help me with the age.
100,000 BTU Bryant serial # 38R 31688

The 31688 is a consecutive number, but the 38R seems to indicate the 38th week of 1964.

I agree with RR - 38th week of 1964.

Thanks, Russel and Bill.