I would like to think that the engineers that designed my engine would know best how to break it in and they say to break them in easy.
On a fresh rebuild I think it is best to run conventional oil in it. Drive the car for about twenty miles and then change the oil to get out anything left over from the rebuild process and then refill with conventional oil since synthetic is said not to let the rings seal properly. After doing and easy break in for 1,000 miles you can switch to synthetic. If the rings aren't sealed by then they won't seal at all. Just follow the break in instructions in your cars owners’ manual.
Just my
