I put a pistol grip on my HD shotgun. It did not stay on there very long before I replaced the wood. The recoil of a shotgun begs for a shoulder to rest it on. I found that the trade in size was not worth the lack of ability to aim.
I have an old wichester ranger model 150 that has a cut pistol grip handle and the recoil is nothing. I can honestly shoot it one handed (not safe I know) and it dont kick hard. I had a 870 with a tactical pistol grip from Cabelas that feels like a true pistol and I loved it.
To have the barrel cut off and recrowned would cost more than the gun is worth. I would trade it or use it for a truck/barn gun. I would like to find a throw away pump like that to leave in my barn. Every time we get a chicken killing critter hanging around I end up killing it with one of the luckiest pistol shots I have ever seen. I couldn't duplicate the shot with a case of ammo.