Joe,
A "taper pin" reamer that has a 1/4" per foot taper will leave a 4" long forcing cone. Before you use it, you must confirm that the taper of the outside of the barrel is less than 1/4" per foot to ensure you don't have a spot thinner than the current corner of the chamber. I believe a Fox has a taper less than 1/4" per foot on the outside. If so, you'll be fine.

Have you given any thought to forming the bulge down using a plug before filing?