The instructions for my Edelbrock said that for the first 30 minutes, the engine should not go below 2000 rpm (vary it like dan76 says) and that the initial run-in should be uninterrupted. If you have a roller cam, this isn't necessary. You should also put in a bottle of GM E.O.S. (engine oil supplement - p/n 88862586) available at any GM dealer. After the run-in, let the engine cool down completely and throw a torque wrench at the head to make sure no head bolts came loose. After this, all you want to do is avoid running it at a constant rpm for any length of time for the first 500 miles.
