Valvoline VR1 racing oil is readily available around here for $3-4/quart (Autozone is 3.06, Kragens 3.95)
Since it doesn't have to meet API standards, it has full comple,ement of ZDDP. Even says so on the case! And my machine shop foreman told me in no uncertain terms to use it on a Dodge 225 we recently rebuilt...that GM's EOS and diesel formulations are also being changed to lower ZDDP.
While I'm using up my Castrol, I do add a bottle of STP which dumps a lot of ZDDP into the mixture.
Note: this applies to more cars than you might realize! Even my 92 Olds is a "flat tappet" even though it is hydraulic not mechanical (vs roller hydraulic tappets on the new cars) and my DOHC SAAB is also flat tappet!
VR1 is available in straight 30, 10W-30, etc. as well but you may have to order it.
FWIW