273 camshaft help?

so I've been working on restoring my 67' cuda fastback for a couple years now and we have ran into a standstill on the valvetrain issues. From what I was told when I bought it, it was overhauled but the work was less than reputable (all main bearing bolts were hand tight) and I cant seem to find the reason for a clatter in the top end. We've already replaced the gears and chain and adjusted the valves to stock setting 10 times over. any help or ideas would be greatly appreciated.