For the initial 500 break in miles following a motor rebuild, my builder has always recommended straight 30 weigth motor oil (non detergent) and thereafter I am planning to go with an oil such as Brad Penn with a Zinc additive.
Why would running a non detergent be good right after a an engine rebuild? I would think that after a rebuild you would especially want to capture and suspend the small metal particles and send them to the filter. If you had a non detergent, i would think the particles would just be floating throughout the engine with no guarantee that when you change the oil and filter your getting them all out of the engine.
Only time to use non detergent would be in a lathe or gear box, where you want the particles to fall to the bottom so there not being pushed through the bearings. Seems like there would be far to many places for the particles to get caught an engine (lifter valley, heads, etc..).