That is a very odd-looking flaring tool!
I have several, including a wartime Imperial Brass. It has two large wingnuts for clamping the die together, and the screw-type anvil, which slides on or off. It doesn't have that handle affixed to the anvil. What does that handle do when you turn it? I'm curious about the purpose. Is that a cam action tighten and quick release? (EDIT: I'm guessing that's what it does. Instead of threaded bolts and wingnuts, you just move that handle to tighten the die halves together or release them. Pretty nifty.)
I've also never seen an Imperial Brass anvil painted red.
As for the "USAAF" marking, I wouldn't dismiss it too quickly just because it was applied in the field with an engraver.
On the patents, Imperial Brass stamped the heck out of their dies with their patent numbers. The wartime dies have several patent numbers on them, as late as 2,370,089, which is 1945. You will also see them with in between wartime patents 2,226,852 and 2,242,831, back to 2,072,559 (which dates to 1937). Yours with a 1,724,697 patent (1929!) precedes all those.
Very cool find.
