I am a big fan of the Griffin Taper Mount, which would be the Plan "A", I believe for your purposes. I have even switched several other brand cans over to run the Plan A, and they get a lot more use now. GA sells a wide selection of brakes for the TM system, with a bunch of different thread specs. The price they charge is generally less than most of the competitors as well. They are turned on a Swiss lathe and the Nitride finish is impeccable on all the examples I have received.
I do think that your doing the right thing getting it switched out. The SDN-6 is a great sounding can and there's nothing out today that really does it a lot better, from a pure sound perspective.