[jeffschevelle]

Rather than someone over-stamping that letter years later, seems more likely to me that either

(A) it was mistamped at Tonawanda and corrected at Tonawanda before shipping to KC, or

(B) it was correctly stamped at Tonawanda as initially built (as a manual engine), but for some reason was changed to an automatic before going into a car (either changed at Tonawanda before shipping, or changed at KC after it got there), and that letter got over-stamped then. July 2 is very late in the production year, so maybe they checked orders vs. inventory and had to change one or more manual motors to AT motors to meet the remaining supply needs?