WW2 Chevys and GMC CCKW used a GM corporate axle and housing, it was not NAPCO in any way. NAPCO tries to steal the limelight in claiming it was the first Chevy/GMC 4x4. Sorry, but not true as the military $$$ had them beat by at least 15 years. Look up Chevy "Banjo" axle.
Real early 1940-41 GMC and Studebaker trucks used a Timken front drive axle similar to the ultra rare pre war 1930's Chevy, and Dodge (perhaps Federal?) prewar military 4x4 trucks.
I am not a NAPCO expert and don't claim to be, but I am a rabid 4x4 enthusiast. I think the closed driveshaft was the limiting factor for NAPCO 4x4 systems so 1/2 ton trucks were never converted until Chevy/GMC went open driveshaft on their product line.
Dodge always had their own 4x4 configurations, after 1940-41; before that they also used a Timken front driveline (VC'S).
