I have seen movies from the 1970 Pontiac assembly line where the engines were spun with electric motors. They were even balanced once most of the engine was put together. Last step in assembly was putting the covers on.
This is a cool 1936 Chevrolet film, there are four parts to it . The engine building part is the best. The guy tunes it using big old screw driver up to his ear.
https://archive.org/search.php?query=subject%3A%22Occupations%3A+Automotive%22
Break-in is just like oil choices, it's your money, do as you will.
Joe
