Those two tabs in the tube can be fairly easily removed with a Dremmel & grinding cone-shaped stone. Just take off as much as you need & most assuredly, do several function checks after ext tube installation.
"figured if the fight ain't over in eleven rounds I'm in deep trouble"
That's for sure & you'd want another 11
Shooting nothing but 870s since 65 or so. Think I'll stick with what I know best.