I'm finding as I research military aircraft radio setups, that more and more there were slight variations allowed to either fit an aircraft's mission, or if supply issues forced them, especially during wartime. Issued in Lu Of , more common in the 40's and 50's, but lasting into the present day. And the US military has pretty much always been good at modifying and re-purposing equipment.
73
Mark Dorney
WW2RDO
"In matters of style. float with the current. In matters of Principle, stand like a rock." - Thomas Jefferson