I run Walmart oil + ZDDplus additive. I haven't decided on a synthetic yet, probably Amsoil though.

ZDDPlus™ - ZDDP Additive for Classic Cars - Agricultural Equipment & More

If you want to have more zinc and phosphorus additives in the oil, then use a "high mileage" oil, they have more additives. The API rating is SL.

The EPA hasn't necessarily required that the additives be reduced. They have required that factory catalytic converters last 8 years/80000 miles. The burned zinc and phosphorus compounds form a coating on the cats, reducing their efficiency. To make the cats last longer, the additives had to go.

H series guys have it really bad with the new oil.