I use a PT-50 on my 2341, and I have a buddy that uses a PT-48 on his 2341. Both of these get that great "tuba sound", and allow extreme dynamics on both ends of the horn...(but mainly the big and bold end)
The new King 2341's have a relatively large receiver that I have found works better with larger shank mouthpieces. Even so, the Conn Helleberg should be fine because it has a continuous taper of the shank up to the cup. I had a mouthpiece with a flat area at the bottom of the cup, and it hit bottom before seating in the receiver.