Talk to a buddy with a lathe. Remember the hardness of the metal used for hte barrell - you will need about a week to cut it with a hacksaw.
Anyway you cut it, you are looking at burrs. A lathe is the best choice, second is to use a shop cutoff saw (bandsaw type.) Use LOTS of coolant/lube so you do not alter the temper of the metal.
I know Brownells sells muzzle crowning tools, I would not improvise here either. Doing the job right in the first place makes it easier to finish when you are done.
If you are thinking that it would cost you more to do the cut work, check with Numrich Gun Parts, Corp. for a shortened barrel that will fit your action. Nomrich often has good prices on the semi-oddball stuff that a few people are looking for and they always wind up with, so it's worth a shot.
FFZ