Zero Clearance valve lash ?

Just because Pontiac's don't have an adjuster and you torque the rocker arms down doesn't mean their at zero lash. They don't use an adjustable nut like a small block Chevy does but a lot of Pontiac guys swap them over to an adjustable nut to properly adjust the lifter preload. That's an old racers trick to get a couple hundred more RPM from them.
Yeah that is what I did, put the lock tights on and turned them just until each valve started to open. Your right the RMP's were quite impressive!