FAIRCHILD (1) Flying Boxcar (N1394N)

I cannot figure out what is mounted as a dorsal feature ...

"The jet engine on top of the fuselage is a Westinghouse J34, delivering additional trust if necessary. The jet comes in handy when taking heavy loads out of small places. The jet-pod has a muzzle up front that opens up for intake air, as soon as the jet engine is started. Since it is so high up on top of the fuselage, the J34 jet engine can't suck up stones and get FOD. This is usualy the problem with jet engines and gravel runways."

See here : https://www.flyingboxcar.com/index.php?page=2

Thank you Viv Pike!!