Need some assistance in locating the cause of a no OP condition on a fresh shortblock. Motor was assembled using the components of another motor ie; oil pan, cyl. heads, etc.... Problem is zero oil pressure to the HPOP. Manual fill starts the motor but LPOP does not feed the HPOP reservoir. Could it be a stuck anti-drainback valve? Going to install a manual OP gauge to check base OP. New gaskets and sealers and parts used throughout the assembly. BTW runs fine before the HPOP runs out of oil supply.