Very good reads, but I'm still a little confused as to the best way to go. I have a moderate build 351C 4V in my 1972 Q code Grabber Blue Convertible that has been driven sparingly over the past 15 years. I run the car hard about once a year. I have not had an engine failure yet. During most of that time I ran 20W50 Castrol or Valvolene. I always added a pint or so of this as well:
https://lucasoil.com/products/engine-oil-additives/heavy-duty-oil-stabilizer. I got hooked on the Lucas Oil Stabilizer when I played with one of those little displays at the local parts house showing how much better the oil stuck to the little Teflon gears when the stabilizer was used. Most people probably don't know what I'm talking about, unless they are an old geezer like me. When I heard about the issues with low zinc, I started adding a small bottle of ZDDP with each oil change. In Birmingham, AL the outside temperature stays hot most of the time when I'm driving the car, so the higher viscosity didn't bother me. I was satisfied with my oil pressure staying around 60 at idle and 80 while cruising. Then I got the idea to switch to low viscosity 5W40 ? Mobil One while still using the additives, and now I don't like my oil pressure which now runs 35 to 60 most of the time. So far the car is not using any oil. I'm thinking about going back now with just 20W50 Castrol. Any ideas?