With many lathes you'll have a difficult time getting the spindle to turn slowly enough in relation to the leadscrew to produce slow twist rifling. The problem isn't gearing, the slots are cut in the quadrant in such a way as to limit the maximum lead possible.
Auxiliary equipment incorporating a worm wheel attached, usually to the front end of the spindle, a worm meshing with this worm wheel, idlers and/or change gears as necessary, and a worm wheel to mesh with the leadscrew are available for some lathes, and have occasionally been used for rifling barrels.
Perhaps this is the answer of a tool and die shop owner, but I'd think it far easier to do the job right if you were to build a rifling machine from scratch. I think that there is a picture of Brockway's rifling machine in Roberts' book the Muzzle Loading Cap Lock Rifle. This will, in my opinion, be simpler to operate well unless you are an outstanding lathe operator.
There may be a bit more information on the old style rifling machines in Dillon's Kentucky Rifle than is available in Roberts' book. Roberts used some of Dillon's photos (with permission). But I don't recall Dillon showing as much regarding sine bar type machines.
Another approach is to modify a long bedded lathe to accept a sine bar attachment. Harry Pope did this. Instead of the straight sine bar used to produce regular rifling Pope used a hardwood patterns having a complex curve to drive the follower as he almost always cut gain twist barrels. A few illustrations are in The Story of Pope's Barrels by Ray M. Smith.
Still another approach is to gear a dividing head to a horizontal mill. This is illustrated in James V. Howe's 2 volume Gunsmithing book (not Home Gunsmithing.) Roy Dunlap in his Gunsmithing book indicated that this method may be more trouble than it is worth. I don't know,I've not tried this, but I've got to believe Dunlap.
If you are well versed in electronics and programming, industrial surplus outlets sometimes have servo drives which were part of machine tools for sale. I've never seen a rifling machine constructed using one of these, but I believe a practical and accurate machine could be made using one of these units instead of a sine bar, and perhaps at less cost.
Best of luck,
Bob