Thanks for your input guys. ByLoudDesign led me to the Servo City site where I got most of the dimensions I was interested in for the swivel ball linkage except for the "shank" O.D. The other dimensions provided, indicate that the 2-56 and 4-40 appear to use the same body with a smaller bore diameter in the ball. If that's the case than what blvdbuzzard is saying is likely correct. There is sufficient material to drill and then thread in a 4-40 pushrod. I was in the same boat as jetmech05 with concern that drilling for a 4-40 rod would reduce the wall thickness to a point that would invite failure.