Has anybody ever thought of finding the drill & tap size for threads closest above the small side of the taper pin holes even if having to up drill slightly and also creating a flat-bottom countersunk hole for a hex socket cap screw of that size tap on the large end size of the taper pin holes and then splitting the rings on the bottom side (perhaps with a hacksaw or similar) to create a clamp on version. Obviously depending on the size of the ole location a round file will likely need to be used to create cross-channels in the bottom side of the barrel for the space where the threads of the caps screws would interfere as long as the cap screws do not protrude too close to the barrel bore and compromise integrity.
