Any "restriction" as in a predetermined additional orifice like a carb main jet etc placed inline to an
oil cooler would simply lower the maximum pressure that can buildup in the system after the
oil pump.
So if you do this, your
oil pressure gauge sender and warning light switch, cutouts etc need to be after the cooler which is then truly sensing engine oil pressure, and not at the oil pump.
Myself, if my engine runs 80 psi cold, then a cooler that is pressure tested to say 200 psi should be enough.
A thermostatic bypass valve allows a small amount of oil to circulate through the cooler as the engine warms, and gradually opens to take more of the flow through the cooler as the oil temp increases.
Allows fast oil temp warm up to, and controlled temps under adverse conditions.
I rather run a custom sump and pickup, trapdoors etc, and run a little less than most do in the engine.
This allows the oil in the engine sump to warm up faster and boil off the acid from each cold start.
My 2 cents.
Gary