You are correct TC. The 54 heater not only had the differences you listed but in addition : the defroster was now lever operated [ not cable operated like the 47-53 ] & now the cable operated the trap door to control the ammount of air that entered the cab.The 54 heaters do not have the little " Harrison " ID plate on the back side, it was changed to stenciling.
I do believe there may be some late 53 trucks that have the 54 heater. One of the 54 heaters I have has a stenciling on the back stating
" H. D.- 206 - 53 ".
