A quick way to identify a hydraulic lifter is to stop the engine with the valves fully closed on any cylinder- - - - -doesn't matter which one- - - -and apply a firm pressure on the pushrod side of either rocker arm with a big screwdriver or a pry bar- - - -like you're trying to force the pushrod back into the lifter. A couple of minutes of firm (but not excessive) pressure will cause the lifter to collapse and a gap of 1/8" or so will appear at the valve stem side of the rocker arm. It will disappear as the engine fires up again- - - - -with maybe a minute or so of rattle as the lifter re-establishes its normal preload.
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!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!