No, with no restriction, no pressure drop. You haven't said what gauge you used while priming?

No. With the oberg setup you are getting more oil to the bearings because it flows freely.

Earlier post... Autometer Pro Comp mechanical.

I still don't get it with regard to the pressure drop. The Oberg still creates a restriction. It flows more than regular filter but it's still there.

Think of it like this. If you took the line feeding the filter and put a plug in it started the motor would you have any oil pressure?... No

Now take the plug out and feed the oil filter with a 1/16" line start the motor would there be any pressure? Yes but minimal.

Now keep stepping your line size up to feed the motor. The more flow you get to the bearing the more pressure you will have... Less restriction = more flow to the bearings which makes more pressure.

Sorry I missed that. That kind of rules out the sender/gauge in boat. The filter will have a pressure drop, but not more than a few psi, especially if the bypass isn't plugged. The fittings, lines, and oil cooler have some restriction and will drop pressure. 45-50 does seem low, but your setup is different than it was on the dyno and you will see less pressure with the added restriction.

Oil pressure will drop as a result of a couple things: more bearing clearance, or an increased demand on the system like oil lines, coolers, remote filters, etc. or both....
The filter is the first thing after the oil pump, but pressure is usually taken somewhere after the filter. If the filter has enough restriction, it can effect the oil pressure but this is seldom the case unless there is something wrong with the filter. Since the pressure is read after the filter, more filter restriction will cause lower oil pressure, just like a clog in the line. However, since pressure is taken before the bearings, (and pressure is simply a measurement of resistance) the more bearing clearance you have, the less pressure there will be, all else being equal.

I hope not. That's WAY on the tight side for a marine engine IMO, especially running heavy oil.

Throwing other things against the wall: Hunk of **** sticking psi valve on oil pump ? Filter ? Hunk of schit at oil psi sender ? Or at gauge since mechanical ? External oil lines on correctly (ie: correct direction) ?

are you sure the oil lines are routed correctly?at this point i would remove the merc system and install a good quality oil filter directly to the engine block and note the oil pressure.if the pressure is still low the next thing i would do is remove the engine and inspect every clearance in that engine.you stated that you don,t know for sure what the bearing clearances were so at this point you need to find that out.i can tell you from past experiance that the electric gauge in the boat do not always tell the story.hook up a mechanical gauge when testing the engine in the boat.good luck and i hope it turns out to be a simple fix.edit in. horsepower1 is correct,the chevy v8 engine will have no oil pressure until the oil flows through the filter and back into the engine.

Did you replace the oil pressure sending unit as part of the build?