Hey Ed:
I also had a low
oil pressure concern. My builder (HRE) used 20W-50 Castrol with some additive (no doubt a thickener). The
oil pressure was never as high as I expected and would show signs of starvation even though I have a 9 quart pan. I decided to go the other way and use a thinner
oil. I replaced the paraffin oil with Mobil1 oil and filter. I used the 5W-30. The pressure was much higher with the 5W-30, it also went up with RPM which it did not do previously. It idles a little over 50 PSI.
For the record I don't have an FE. My own theory is the thinner oil is better able to go through all the plumbing and cooler than is the thicker oil. Mobil1 comes in many viscosities, 0W-30, 0W-40 (Porsche recommends for its newer cars), 5W-30, 10W-30, and 15w-50 (Porsche recommends for its older cars). Ford Motorsports recommended the 5W-30 to me. I also like the feeling that the oil gets up and goes during cold weather (I live in Connecticut). Good luck!
Bob In Ct