ticking engine sounding like diesel - 560SEL

[emmydotnet]

ticking sound gets louder with engine rev. using a stethoscope, i have isolated the location on cylinder 1 location. ticking sound gets very pronounced when stethoscope is placed on exhaust manifold on cylinder 1. rebuilt heads have 20K miles on them. chain is also new. what are the suspects in this case? lifter, valves, tensioner? thx