I'm new to the high horsepower BBC and have one in a S/C dragster. I was concerned about the oil pressure when I was running Castrol 15/40 mineral oil (10 - 15 pounds pressure when hot at an idle). So I changed to Pennzoil 25/50 GT Racing mineral oil which is about 75% the cost of the Castrol stuff. I raced last weekend and at an idle, when hot, the oil pressure was 30 - 35 pounds and at high RPM it was 80 pounds plus. I am going to stick with this oil and see how it performs.
Here's the oil:
http://www.pennzoil.com/#/motor-oil/racing-motor-oil/