There is no valvetrain adjustment on a standard Pontiac engine.

Nuts on the rockers are tightened to the specified figure, and that's that.

If you have roller tip rockers, adjustable drivetrain, replacement rockers or pushrods, incorrect lifters, incorrect installed valve height then you will experience valvetrain noise.

Pull off a rocker cover and post a couple of pics.

It's not a Chevy, and adjusting it like one won't work.