Oil change

If you need zddp get an oil with it blended in
adding zddp to SN oil can actually lower EP
even in the south 20-50 is too thick cold and you do not need 50
0w-30 should work or 0w-40
most of your wear comes when cold
BTWmy 68 Polara as over 300k
been using 0-40 last several years
change it every 5k with carb
Dakota with EFi once a year-
Natural gas oil is oh so much better than dino oil check out the data sheets
I think that 15-50 is for supercars, late vetts take 0w-40
see that column with the phosphorus- that's what your are looking for
after break in and without really stiff springs I think 800- 900 works fine
Oil is constantly being re-formulated stay on top of it