lifter issue?
The lifter pistons should be "rock solid" for a long time. I can start my engine after sitting for 3 months and no tapping sounds which means that all the lifters are still pumped up. I'm not aware of anyway to measure the actual cam lobe without removing it from the engine. You can measure the effective lift by putting a dial indicator on the lifter. Putting it at the rocker arm takes into account the rocker arm ratio which maybe not be, exactly, the advertized ratio, eg. 1.5.
Terry