Brian
Your problem sounds like leaking valve seal how is oil consumption, any blue smoke at start up. as far as the valve tapping if you take a hammer handle and push down on the lifter if it is bad it will compress but I believe you will find that is not the case.. what kind of fuel are you running on my 560 if I use off brand of 93 I find my valves start to tap I run shell v power or BP that solved my valve tap problem.. Also there is noise from the chain the engine sounds like sowing machine that is normal. The missing problem could be caused by ingintion wires, cap , rotor. If they have been changed its injectors. If they are orginal they will need to be replaced, but before try cleaning with techroline injection cleaner.. its process of illumination... let me know i have been all through this engine ..