It's possible you've got an engine with hydraulic lifters. Setting solid lifter clearances on a hydraulic-lifter engine guarantees lots of valve noise.

Try getting the valves on a cylinder closed on the compression stroke, with the engine stopped, and apply a firm, steady pressure to the rocker arm with a pair of vise grips, trying to move the tip of the rocker away from the valve. If the clearance increases noticeably after several minutes of steady pressure, you've got hydraulics. A collapsed hydraulic lifter with the cam on the base circle will have about 1/8" of clearance between the rocker arm and the valve stem.
Jerry

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