SCOBRAC,
the engine is original without hidraulic lifter galleys. A solid lifter HP engine throughout.
I replaced the filter today with a Purolator, but when starting the engine,
oil pressure would not shoot up instantly as before, now it creeps up slowly,
I'll take the Melling HV pump out tomorrow and check if it is drawing air from somewhere. I remember that the pickup was touching the windage tray when installing it, and it may not be bolted down flat on the pump surface.
More news tomorrow.