Who knows factory cylinder heads ?

A 50's era Chevy truck was probably a solid lifter engine. You Mopar is a hydraulic lifter engine, the lifters pump up when running so you don't really hear them. If you do start to hear them, as stated, you have a lifter going south, or a cam lobe. It's messy to do, but pull a valve cover & see how easily you can spin the push rods with the engine running.