Need help understanding date codes of "12JB" from a pair of manifolds said to be taken off a Hemi `Cuda that had less than 10 miles on the odometer when the car was converted to a race car in Mustang, Oklahoma. I thought the format was month, day, year "mddy", like B159 would be November 15, 1969... but that doesn't work in this case.

Thanks for any guidance...