I agree with mixtroy's thesis that the best defensive players would make the transition the most easily and, as zubinsum says, great defensive 3B would do best of all. Chances are that's still not very good by WIS standards.
In RL, there is no position that converts particularly well to a catcher's specialized skills. Third basemen need accurate rifle arms, but that is just one of the tools of a good catcher. Intelligence, game knowledge and the ability to handle pitchers are specialized skills virtually unique to catchers (and theoretically coaches and managers) and, unlike the short, squat Yogi Berra types of the past, the physical prototype for today's best catchers (big and strong or big and rangy) isn't perfectly matched by any other particular position -- first base and pitcher probably come closest.
RL conversions to catcher from some other position are less common than from catcher to other positions but, at least anecdotally, it seems most common to convert third basemen and shortstops. Lance Parrish was converted from 3B, Gary Carter from SS, Jorge Posada from 2B and SS, Victor Martinez from SS, Brandon Inge from SS, Russell Martin from 3B and Bob Boone (I think) from 3B. I think Jason Kendall may also have started as a middle infielder.