In response to item B, a 'What-is-it?' in the June 2002 issue of Farm Collector: The device is indeed magnetic and the source of the name 'magnetron,' which is the heart of all our current microwave ovens. The device pictured was the magnet for a military radar magnetron, which is a form of vacuum tube. The tube here was made of relatively soft metal and is not shown in your picture. The adjustable gadgetry between and below the pole pieces serves to adjust the size/position of the vacuum cavity, which sets the desired frequency to resonate with waveguide output to antenna.
If you think this all sounds magical, then read up on parametric amplifiers, which juiced up the returning echo signal. Tuning those was a black magic art. Ahh, the memories!
Growing up in rural Tennessee in the 1960s, I developed an interest in radio and had crystal radios, home-built transistor radios, modified tube radios or whatever I could find to listen to radio stations around the United States and the world. This led me into electronics in the U.S. Air Force, where I met the type of gadget shown in your magazine.Bob Payne