Before you remove valve covers to chase a possible click, try shortong out the plugs one cylinder at a time to see if click goes away----could be loose/broken piston skirt or possible bearing / wrist pin starting to make noise--usually shorting out the spark the noise goes away---------

On adjusting the valves----you are going to spray some oil around so the cut out valve cover used to be common---also there were some clips to put on the ends of the rockers to stop the spray---

Roger, finger tight on the nut and set screw are aftermarket items--stock stuff will be self locking rocker nuts and they will be hard to turn. also a stud could be pulling out of head casting--