Bob,
Your engine builder is right - for the most part... We use nothing but -12 or larger lines for
oil coolers and remote filters as there is far less pressure loss due to the parasitic drag in the smaller hoses and fittings.
Where we disagree:
The coolers on a Cobra are well exposed and it takes very little movement through the air to have a positive affect on the cooler.
The rest of the story lays within use during cool/cold weather. There are
Oil Cooler thermostats out there from companies like Mocal that are good, but not up to competition use due to the nature of the smaller passages in the thermostat housing. Best advise is to kep the RPM's down until you have some temperature in the
oil - this is regardless of your using an oil cooler or not.
Guys with 302's - this information is all particularly relevant to you since you typically cannot get away with running a high volume oil pump with a roller cam.