Ill take a shot at an answer. Perhaps Johnny Graybeal can correct me.
Perhaps during the timeframe you mentioned, the 2-8-0 engines no longer
were being used in the Johnson City yard or in any other connection with
the standard gauge operations, so the three-way coupler was removed and
placed on one of the 4-6-0's which interconnected with both standard and
narrow gauge cars. That doesnt answer the resulting drop in coupler
height, but could answer the changing of the coupler.mw