I gave better information than we got. :D
The Castrol GTX 20/50 in Florida was a safe answer.
Having run it in every new and classic for over five decades without failure is proof enough for me.
If the chemical makeup of Castrol GTX had stayed the same for the last 50 years you’d have a point. It hasn’t.
Pretty much all the major oil brands have dropped the zinc content of their non-specialty oils in the last decade (or two) as most cars run roller cams. The Castrol you buy off the shelf today is not the same oil it was 50 years ago, that’s a fact.
For the most part, only specialty oils still have appropriate zinc levels for a flat tappet cam.
Now whether the OP has a flat tappet cam or not, well who knows.