Need help with oil options

You have to use a zinc additive if you are running a flat tappet cam. NO exceptions. Use a mineral based break in oil initially and for the first 1000-2000 miles. Using a break in additive with regular oil is to take an unneeded risk. Mineral based oils help the gaskets seat better than a synthetic. You can them switch to a synthetic oil with a zinc additive afterward.

There's no doubt that synthetic oils hold up better than conventional oils. With multi-weight oils, synthetics start out as a base at the thinner weight with additives to increase the viscosity in response to heat. Mineral oils are the opposite, starting out as a more viscous weight with additives to decrease viscosity at lower temperatures.

The problem is that 95 plus percent of engine wear occurs at startup when the engine is cold. Conventional oils quickly lose their low viscosity properties while synthetics preserve cold startup protection.

Engines don't fail because the viscosity is too low, but because it is too high. High viscosity oils increase fuel consumption and are only useful to help reduce oil consumption in engines with loose tolerance valve seals and rings.

If you've rebuilt you engine using modern components, forget 10w-40 and 20w-50. Use a 0w-30 or 5w-30. If you are ruinnng a roller cam and roller lifters, you can forgo to zinc additive.