28in barrels would not be strange. No choke is though, when it says choke on both barrels. They could have been opened up at one time.
I highly doubt that gun would have came with such a forearm. I would bet those markings you talk of on the barrels are not from a beaver tail forearm at all but rather from a leather handgaurd. The handgaurd has a metal piece of spring steel in it that keeps it tight on the barrels. Taking it off and on over the years would result in a wear pattern such as you speak of.
