head thickness valve train noise

ok guys noob questions here got my motor in the car (340) and its not running right it has a tick like a bad lift. has a 507/510 comp cam adjustable rocker arms with x heads, check lash and everything few times and still no luck my question is can i check if my heads been milled down on the motor or do they have to be off? if i have adjustable rockers would the head being milled down matter?