Thanks for doing this. Have you checked out the reamers by PTG? They are also going to produce conversion reamers that do not cut on the shoulder so it will not affect head space. Seems like a safe way to convert a chamber.
http://www.quarterbore.net/forums/showthread.php?t=4642
On edit. rereading this I realize that it IS a PTG reamer that you used. So, what do you think of the idea of using a conversion reamer that does not cut the shoulder?