Don't know what to tell you about the valve train. If that is is a Comp Extreme Energy or what ever they call their most aggressive lobe profile hydraulic cam, they are noted for being noisy.

The only things I can think of besides a FUBAR oil filter that can make oil pressure come and go like that is a sticking relief valve or a spun pump drive that is now using friction to turn the pump.

If you changed the pump when you built the engine, did you disassemble it and clean it? It's amazing the machining trash you will find inside a new oil pump that can jam the rotors and twist the drive or hang the bypass.

Kevin