I have a boat with a 460 and I lost oil pressure was having problems with water in the oil and replaced all the gaskets from the heads up and on start up I'm not getting oil pressure, I'm spinning the oil pump with the distributor out manually and I pulled the line off of the remote filter housing and it's moving air in pressure and vacuum but their is no oil making it to the filter

 

Had a 302 in a boat. Oil pickup tube came loose and no pressure but pump turned.
Had to take engine out to find that problem. Maybe yours also? JAT

 

Just pulled the motor yesterday snapped rod and it hit the oil pick up tube problem found thanks for your help