It's about the ball on each end fitting/matching (1) the lifter cup & (2) the rocker & (3) side clearance to the head wall & B3 racing has the good info & checkout the scott foxwell utube video on rocker geometry to confirm you have the right length on the pushrods (or to know the right length dimention before you order if need be). I cant say 3/8 is needed (maybe maybe not) but they would be stronger & OK if they clear the wall & match the top/bottom recesses. EDIT the video is straub technologies & is 12.01 minutes long to confirm you have the right one