Your barrel was cut down, it used to have a C-lect choke on it. the bright side is that it looks like the barrel was cut right behind the choke. I say, drill it, tap it, and install a bead, then look for a used M 500 barrel with the Accu-choke system. Or you can use your 870 for birds, and turn the WF into a deer\bear gun.
It is the Westernfield (hardware store brand) version of the Mossberg model 500 ab. If you are looking to find out more about your shotgun, contact havlin sales. Victor Havlin is the president of the National Mossberg Collector's Association. They may be able to help you find a DOB for your shotgun.