I would use a "break-in" oil specifically formulated for the engine on initial start up. Brad Penn and Joe Gibbs Driven offers break-in oil.
Remember to prime the engine/oil pump. When you see oil at the pushrods, stop, then turn the engine 1/4 turn and repeat. Do this for a complete 360 degree spin. This gets oil to the entire system and works out any air.
Here is a break-in procedure once engine is first fired up and then when you take it to the road.
https://www.jegs.com/InstallationInstructions/0/059/059-hp291p.pdf
Here is a 2017 study on different types of oil and wear characteristics in a modern engine. What may be most important is the Zinc (ZN) content. Not the T6 Shell Rotella as compared to others.
https://jalopnik.com/why-expensive-oil-is-a-waste-of-money-1797241527
Synthetic oils are better used with tight clearances and perhaps no so much with the recommended clearances that engine specs of the day had us doing. Found this snippet that suggests synthetic oils may not be good for older engines because it is "slipperier," which means it may not cling so well where we need it to cling. I have read this of synthetic gear oils used in the older type manual transmissions and that it lacks the "cushion" that conventional oils build up as they cling to the gears - and you get gears clashing and harder shifting.
"While synthetic oil generally protects better over a longer time, it flows more smoothly than conventional mineral oils – and for an older engine, this can mean a greater chance of grinding gears. For this reason, most manufacturers and mechanic recommend conventional oil for owners of older and more experienced engines. The slower flow of a conventional oil promises better lubrication for aging engines and can mean the difference between your engine lasting for the long haul and giving up before it is really ready to go."
I have also read that the synthetic oils, because they are more slick than conventional oils, can seep out from bearing surfaces if a car sets for extended periods - like when some mothball their cars for the winter or perhaps only run them after sitting a few weeks at a time. Again, might be due to larger bearing specs/clearances often associated with our older cars.
So it seems as always, there are indeed many opinions and a host of comparisons to support or refute the use of conventional oils or synthetic/synthetic blended oils. I personally use conventional oils in my older cars. Many of the oils still have the Zinc in them and are said to be OK with older engines. Too much zinc can also be problematic. Rislone makes a zinc additive and I have used it in several of my older cars that use conventional oils. Perhaps you won't need the entire bottle each time, but I can't see how it will hurt if you added 1/2 bottle to each oil change - unless you know the oil is formulated for older engines like the Brad Penn/Joe Gibbs Driven, or the Rotella.
