Current car oils have around 500-600 PPM zinc. Most say you need 1100 - 1300 with a flat tappet cam. More with high spring pressure. Always.

Cam companies, engine builders and car mags have written about this. Lots of posts about flat cams kinda prove it.

There are lots of solutions to this folks have used. Adding ZDPP or GM EOS to regular car oil is one. Some 20W-50 racing oils have higher zinc (and some dont't I believe). There are speciality classic car oils and 4 stroke motorcycle oils with high zinc.

I choose diesel engine oil. Rotella T in 10W-30 or 15W-30. Its readily available and reasonably priced. It still has 1100-1200 PPM zinc. I add STP for insurance. For break in add EOS, ZDPP or STP.