dublenaught,
Use the best detergent oil you can. A 30 wt would be fine. The detergent compounds in motor oil will scour the insides of a dirty engine to a minor extent, but their main purpose in life is to encapsulate all the junk in the oil, and hold it in suspension until it can be drained when the oil is changed.
There has been lots of talk about cam/lifter wear resulting from decreased levels of a critical anti-wear compound in current motor oils. If you have installed a new cam and lifters with this rebuild, it might behoove you to read up on this subject and possibly break your new engine in properly with a additive or motor oil up to this task.
The switch from a non-detergent to a detergent in a old dirty engine was reported to plug the filter as the new detergent oil scrubbed the interior of the engine and dumped all the crap into the system, plugged the filter and choked the oil flow to death. I don't know if this actually happens, but with your new, clean engine, you're safe.
Stuart
