Bill and Jim, in looking at a few online catalogs, Midway didn't seem to carry this type of tool for shotguns. They had them for pistols and rifles, I believe, but not for shotguns.
Brownell's has something that I think might be it. It doesn't give the O.D. of the reamer but it has the 55 degree angle and it does have a pilot.
I'm guessing they don't give the O.D. because of all 12 ga. shell head being the same. I wish they would give it for the chamber size because I would think you would want that to be very close.
Again, I think this might be it.
http://www.brownells.com/.aspx/pid=5164/Product/SHOTGUN_RIM_CUTTER___HEADSPACE_RING#
