Jerry, 28" barrels were common, with your choke configuration it could have been special ordered for someone that was a grouse or woodcock hunter. Most "elsies" came through f/f unless ordered elsewise. Since most of these grades were "hardware store" guns, placing an order through them or buying off the rack was common. As far as the markings, I'd be guessing, but they might be marked that way for assembly, c-c, d-d, etc., this way they wouldn't get misplaced for soldering.