A lathe is a good idea, but very expensive. You need a reamer to open up the muzzle end, and the appropriate tap for the thread/style of chokes you intend to use. If I'm not mistaken, Brownell's has the reamer and taps together as a kit.
What you need is tools with interchangable pilots. The pilots need to be the specific diameter of the bore; this prevents chatter and helps you keep the tool straight.
In theory, you could possibly do the work by hand, without a lathe. If you take your time, pay attention, and go easy you should be able to do it. If it walks or goes crooked, the barrel is done for. This is something that I have contemplated for a while, but haven't done yet. I have thought about this and forcing cone reamers, bore reamers, and the like.
Call Brownell's Technical line and talk with one of their 'smiths. They might be able to steer you to the right tools and even offer some helpful advice.