Seems a tad low..my street engines in traffic at 190 degrees at idle run 25-30 lbs.. my first place to look would be the lifter bores..nobody ran a ball hone through the lifter bores did they?? your lifters themselves are they a solid body or barbell shaped ?? I've lost as much oil pressure as you are describing when I've used the non solid body roller lifters or solid lifters.
