Cat D6C 1976 10K, How to add additional 3rd valves

Cat D6C 1976 10K, How to add additional 3rd valves. Dad wants 2 to run a pull pan and now wants a Rome Disc. I wonder to be proper would that be 3rd valves or 3rd and 4th valves. Thanks. P.S. The fuel leak seemed to stop for now (still scratching my head on that one). [/I]

Cat D6C 1976 10K, How to add additional 3rd valves