I use non-synthetic Valvoline VR1. It has 1400 ppm zinc and 1300 ppm phosphorus specifically for flat tappet engines. VR1 comes in several weights and in either synthetic or non-synthetic.
I believe 1200 ppm is generally considered minimum ppm zinc for flat tappet engines.
Last edited by Axis_of_Evil; 04-10-2012 at 01:26 PM.