Brendan - You have the decoding dialed in.
Of note is the fairly low production number. They actually started at 1001 at each plant, so yours would have been the 6241st truck (that's of all trucks, not just 1/2 tons) produced on the Janesville line. That equates to a fairly early in the model year build and pretty much coincides with the casting dates on your transmission too.
FYI - Last fall I came across and acquired a Chevrolet Dealers "Confidential Price Book Cars, Trucks & Equipment" for 1940 which now resides in my Stovebolt Library. It came from a dealership in Oregon, MO and has a ton of original documentation, letters, order sheets and sales flyers for Chevrolet and aftermarket accessories. If you are interested, perhaps I can take pictures or scans and share them when I have an opportunity. Since this is kinda swinging off-topic, send me a PM and we can chat further on this topic.
