Can't tell for certain from the photos which rocker studs you have, but those are adjustable poly-lock nuts you have there. That means you have the ability to positively adjust your lifters.
In order to get a positive ID on the studs, you will have to remove one and see what the stud looks like. If the threads at the top are the same size as the rest of the stud body below the threads, then you have 7/16" "BBC style" studs --- and that's good. If the threads on the top of the stud are slightly smaller than the stud body and you can see a definite shoulder where the stud necks down to the smaller thead size where the threads begin, then you have the factory style Pontiac bottleneck studs.
I assume you're running hydraulic lifters? If so then you don't have to get perfect on the adjustment. What you can do is take a Sharpie and make a mark on the rocker nut and a second corresponding mark in line with that mark somewhere on the head that lines up with it. Put a wrench on the outside hex head of the rocker nut to hold it so that it can't move while using a hex key wrench on the inner lock nut to loosen it off. Then, carefully remove the rocker nut wile counting the number of turns it takes to get it off. When you're ready to reinstall it, screw it back down exactly that many turns until your marks are "not quite" lined up again, then tighten down the inner lock nut snugly, and finally use a wrench to turn the outside of the nut until your marks line up. This gets the inner lock tighter than can be done using the hex key alone and makes sure it'll stay put.