It looks like the 1941 Bell design was the subject of a Modern Mechanix (March 1948) cover as a 'Convertible Jet Helicopter'.
The title "Convertible JET helicopter" can be misleading. In Bell's patent n° 597.246 (Application date: May 23, 1945. Complete specifications accepted: January 21, 1948), the powerplant was a double-row radial piston-engine driving the contraprops.
Interesting to compare this design with Professor B.N.Yurjev's KIT-1 STOL project dated 1946 and powered by a Klimov VK-108 piston-engine.