Grinding, " diesel " noise under valve covers

UPDATE!!!!!!!
So, I warmed her upto around 180 and a Lil less... A Little noise may have disappeared. Still have a "diesel " noise, not as pronounced, ( maybe) lol. Here's what the mech stethoscope " told me", sound is loudest on top of steel " Direct Connection" re pop covers. Same sound on rocker shaft. MP HD rockers... a .002 feeler gauge will drag through some pairs, some not, depending on position when placed next to spark plugs, just kinda a " wirring" mechanical sound. On one, I may have hit the plug, I dunno where (it was getting dark, under power booster) but it Was Loud! Repositioned, and was the same.as the rest.....
I think it's piston slap. Is the car where you can actually drive it and get it heat soaked really good? If it's quietening down at all, I vote for piston slap. IMO, that's an acceptable noise for a true HP engine to make. Not necessarily "wanted" but acceptable.