As the proud owner of at least a couple of dozen old Polychoked guns over the years,,,,my first advice is that if works all right, then leave it alone and don't worry about how long the barrel is. The only, only trouble I've ever had with a Polychoke was the thing not shooting to point of aim, and then you've got to bend barrels to correct it. When they shoot straight, and most of them do,,,,it's a wonderful thing to have on your gun. They are ugly but they work.
To each his own. The idea of spending perfectly good money to shorten a good Polychoked gun,,,,that could very well be invested towards the purchase of yet
another Polychoked gun,,,,is foreign to me. (But of course, I'm a shotgun addict. If I was a drunk I'd be laying on the gutter in skid row.

) But if somehow I would spend any money to mess with a Polychoked gun,,,,I'd spend it to have a sleeve added so it would take the standard Invector/Mossberg/SKB/Winchoke tubes. Then you could add a Poly II,,,, or better yet,,,start playing with a bunch of cheap choke tubes to see if any are much better than the other. I'd put in the standard choke tube because there are so many of them out there, and you wouldn't want an "overbore" choke tube anyway.