Turns out the auction was on Labor Day. My buddy was able to attend, and sent me some additional pics from the day of, along with some notes:
1. The tag is supposed to be its museum tag, from when it was in "the High Standard museum." (My googling has not turned up any such museum, past or present, for whatever that's worth. Anybody got info?)
2. It is rifled all the way to the end of the cooling fins.
3. The magazine holds 100 rounds of .45 ACP, which is why the cooling fins were included. They were, apparently, not a later addition. The "clip" on the side of the magazine is the crank to compress the spring for loading - the auctioneer pulled it out to demonstrate, and it was stiff enough he had to borrow a Leatherman and use the pliers to pop it loose.
4. It has no markings whatsoever anywhere on it, and was apparently designed by a single engineer. The auctioneer didn't know the engineer's name and said he thought it had probably been made in the forties; museum paperwork was on its way from somewhere in Illinois that he said might shed light on both.
5. It failed to sell for $7,500 because of a reserve placed on it by the seller.