If it quiets down after warming up, he's got a leakdown problem that adjusting isn't likely to solve. Wherever an engine stops there are going to be at least a few valves in the open position. After a few hours or days of sitting with valve spring pressure against the lifter it's going to leak down. It will take a little while after startup for the collapsed lifters to refill with oil and purge all the air out. He might want to try running a solvent-type oil additive for 500 miles or so before his next oil change to try to dissolve any gum or varnish that's accumulated in the lifter check valves, then do a hot-engine oil change. We used to use stuff like Casite Tune-Up, Wynn's Friction Proofing, or Bardahl Engine Treatment for that, but I'm not sure any of those brands are still in business. Half a pint of Diesel fuel or Mineral Spirts added to the crankcase 500 miles before changing oil will do about the same thing.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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