Started my 340, IT KNOCKS! fresh rebuild HELP!!

my engine had a knock like that,turned out to be the non adjustable rocker arms hitting the valvecovers.1 rocker on each side hit the baffle? area.I guess the gasket flange was crushed or something.It had a very solid sounding knock,not a tinny knock like i would have expected.Took the covers off and all sounded good,so i went with some antiquie cal customs.Also,Forged pistons make a pretty serious knock sound until the engine warms up