I can't speak for the Sr heads
. Mine are the Jr's
. My Jr's had 7/16-14 holes tapped in them for the studs and I used these...
The 1.9 Affective Length studs will bolt up and actually work with my Juniors, BUT the portion of the stud that lies inside the rocker would be all threads - Poor application. The longer (more expensive) studs allow for more of that portion to be shank (no threads), but leaving just a few in there so you don't run out of threads for tightening the poly locks on. I assume ALL roller rockers are designed to ride mostly on the shank of the stud, not entirely on the threads. The threads are always slightly smaller in diameter than the shank. How important is this? - I don't really know, but my gut drives me to do it the way I do it.