This was the basic design of the KM & WP dryers from the beginning until the early mid 60s. You are right that it was not as efficient as the newer design with the solid back bulkhead, but it does have the 37,000 BTU burner.  In a few years, Kenmore would have the modulating burner valve which contributed to faster drying because it held the temperature steady instead of allowing the peaks and valleys in drying temperature when the burner cycled on and off and the heavy metal disc thermostat had to cool before the burner would cycle back on. 

John, Combo52, rebuilt a Kenmore dryer of this design for me and he put felt strips behind the drum to help direct the hot incoming air through the perforated back of the drum and into the tumbling load and another set of strips around the exhaust port to hold the hot air in the drum longer. It really contributes to the efficiency and speeds up the drying.