clattering---low oil supply

high oil pressure/pegged guage---oil not getting somewhere

have you pulled any plug wires one at a time to see if there is any difference????

402 pretty old engine---if its wrong application cam you could get your symtons

Worn lifters/ bosses---oil leaks out of galley and takes a bit of time to pump up--chev added vent holes to front galley plugs to bleed air from lifter gallies

hitting valve covers??? why was that? what do you have for rockers/ valve covers???

Dist where it passes thru lifter galley blocking oil flow or leaking it down???