After looking at all your pictures, I feel that you have what I call a "2nd Model Utica". The 1st Model Uticas had a steel trigger guard, and a slim trigger. You are correct, saying your guard is an alloy. They were painted black over bare metal, with no primer coat. You also have a color case hardened receiver. This CC procedure did not start until after the production was moved to Chicopee Falls in 1947. At some point at Chicopee Falls, the "B" suffix models started with the internal hammer. It is my opinion that the Utica barrel was moved to Chicopee Falls and assembled as a complete gun at that time. I have seen a few other early guns with the CC receivers. The picture does not show, but do you have a steel or alloy safety button? The very early ones are steel. A weak point in the design of these guns is that stocks tend to crack where they meet the receiver. I strongly suggest glass bedding the inside of the stock before shooting it. Also, I suggest removing the stock bolt and cleaning the threads as needed, and put some grease on the threads. This will prevent it rusting to the frame. Thanks for sharing your gun with us. It is of a far better quality than so many other single barrel shotguns on the market today.
