Well, a stock Jimmy pushrod is 12 and 13/16ths inches long and the head has a .550 inch hole for it to pass through. One would have to be very careful to use a cam that will match the lifter material as Jimmy's used both steel and cast iron cams throughout the years. Tom Langdon at Stovebolt would be a good person to ask. Personally, I'm sticking to the 1 inch roller lifters on my work bench and with Jesel style rockers. Good luck