Along the bearing c-clip to c-clip. The stocks move the same. Put your fingers on the end where the c-clips are and you can move the rocker body side to side.

 

I figured I'd give an update:

I ended up ordering new rocker stands: which seems to have done the trick.

The rockers now have more of a centered position over the valve stem.

Comparing the old stand to the new one, it almost seems like it was a bad cast from the factory: the stands themselves had dull edges, as if the aluminum never got all the way into the mold.

It seems that the rockers were that way the entire time in the original head: the wear marks on some of the rocker tips were towards one side, while the other side looked like brand new cast metal.