Zinc Rich Oil for Flat Tappet Cams

I don't like the idea of 15-40 diesel oil myself. I don't need the viscosity and Diesel oil has more ash in it. That's supposed to cause piston deposits. Some things I read don't like the additives because they might not mix well and/or stay suspended in the oil. The best bet would be to use oil specifically formulated for older engines with enough zinc and phosphorous in it.