I have a post 1971 Win 101 12 ga. with a serial number beginning in K. It has full and mod. fixed chokes and can shoot 2 3/4" or 3" shells. Has anyone any experience with installing the Brielly Companion or Side Kick tubes in 20 ga. I would like to use the gun for skeet and since it can't shoot steel shot I cannot use it for migratory birds. (haven't used the gun since the lead ban came into effect). Are there other tube manufacturers?