Try doubling up on the gaskets temporarily to see if the noise goes away. That won't be a permanent fix, but it will help in diagnosing the problem. Older Oldsmobile engines used to have the same problem when a high lift cam was installed with stock valve covers. There was a set of valve cover spacers available for those engines, but I'm not aware of anything similar for small block Chevy engines.

If you want to keep those valve covers instead of installing a set with more clearance, you might try a slightly shorter pushrod to drop the pushrod end of the rocker down a little. About a -.060" length pushrod could be installed without severely affecting the geometry of the valve system. That's just under 1/16", but it will make a noticeable difference in the rocker arm/valve cover clearance.
Jerry

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