You might find some charts on one of the South Bend lathe sites, yahoo group or even the SB section on Home Shop Machinist forum. Pretty sure as Hercus copied SB to a tee the gearing would be the same.
Hercus are still in business and still reconditioning the 260s so they could probably tell you. And there is a very enthusiastic fellow selling parts for the older Herci who might be able to help too.Here **LINK**