engine break in

If you built your engine with moly coated rings the rings are seated as soon as you start the engine. If they aren't then the wrong finish was put on the bores when the engine was machined and it will take quite a bit of time for them to seat, like several thousand miles. If that is the case you also have lost the benefit of the moly coating because the seating process has worn it off.

Taking it easy for a few hundred miles but still varying the rpms will wear in timing gears, the oil pump drive gear and give you a chance to make sure everything is tight and there are no unusual noises. After that it's ready to go.