Could a head gasket cause a tapping?

[Ieatcamaros]

I did prime the engine prior to start up and had oil flowing all the way to all the rockers

Yeah, but did you prime the lifters prior to installation? If all esle fails, you will just have to keep doing the trial and error my friend. You swapped the rockers, but did you swap the pushrods along with them? I doubt it makes a difference, but you got to try everything. Try switching the heads too. But my money is on the lifters.
Oh, and what method did you use to "adjust" the valves.