Sudden loss of oil pressure in fresh built 8BA engine

[ford1933-2008]

I have just completed a rebuild of an 8BA. At start up oil pressure 40-60psi, several starts later, same oil pressure 40-60psi. Running a new melling oil pump. At last start this afternoon, no oil pressure at all. Removed oil gauge line from rear of block and cranked over the engine, no oil pumped out. Sump has oil and at full on dip stick. Never had this happen before in all the builds I have done (20+ over 7 years)

Any idea what the issue might be? Oil pump drive/shaft issue? Cam shaft oil pump drive gear?

Any assistance would be greatly appreciated. Thanks David