I had looked at the Briley system earlier ... and that would certainly fill the bill. However, adding up the cost of the extension, a Briley choke tube, threading the barrel, new bead, etc. - well, I'm at $295 plus shipping. I'm sure they do excellent work, but that's a bit more than I wanted to put into the barrel.
And, no, I guess I don't really need to have the barrel cut down. I just figured that if I was going to spend the $ to get it threaded, and I wanted a new (larger) bead anyway ... I might as well spend a bit more to make it look nicer. But, functionally, the extra screw hole wouldn't hurt anything.