Are the lower brass cam adjusters installed correctly? Are they worn out? Did the brakes hold adjustment before this? Were the shoes installed correctly?
Also, I have read other threads where some of the replacement brake shoes being made today DO NOT have the lower holes for the lower adjuster correctly located. Compare your new news with your old to see.
Also, read all this info.
https://www.google.com/search?q=1940...hrome&ie=UTF-8
According to the instructions above what you say here is incorrect.
"Second, the instructions and theory on how to adjust is straight forward – adjust the bottom then the top, then repeat until the shoe is centered".
STEP 1 Directions say to adjust the top cam first, then the bottom.
Here's how I always adjusted my 40 brakes. I used a bathroom scale, a short piece of 2 x4 between the brake pedal and a piece of plywood against the front of the seat bottom to achieve poundage required.
Just for the heck of it, very carefully run through the adjustment procedure with the drum removed and see what is actually happening, GO SLOW and WATCH CLOSELY. Make sure emergency brake is released. Hope this helps.