Define "break in". Perfect Circle piston ring company used to recommend 10 full throttle accelerations from 30 to 50 MPH in high gear to seat the rings, but that assumes a proper cylinder prep and assembly was done. Most oil use after a rebuild can be traced to improper cylinder prep- - - -excessive taper, glazed cylinder walls, and/or incorrect honing or cleanup of the cylinders during block prep. Using 30 weight (maybe "non detergent") oil for "break-in" went out of favor at least 50 years ago. There are at least a dozen ways to mess up a "rebuild" with improper assembly, block prep, or other errors. Loose intake valve guides are usually the cause of a smoky startup- - - -oil drains down the valve stems and puddles on the back of the valves overnight, then it gets burned the next time the engine is started.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!