Originally Posted By: SumpChump
Any oil on store shelves these days with zinc protection for ‘86 Chevy 305?
If you really think you need a lot of ZDDP, Mobil 1 15W-50 has it and it explicitly claims to be for flat tappets among other applications.
A good modern synthetic 5W-30 could be fine. I wouldn't go with conventional 5W-30 because of possible shearing. Other options are Mobil 1 0W-40 or Pennzoil Euro 5W-40 if xW-30 is too thin for this car or oil consumption is high.
Unfortunately, the CK-4 HDEO's no longer have a lot of ZDDP. I would go with a PCMO, which is formulated to protect the gasoline engines better, including in the wear department.