Im currently running in a small aeroplane engine (2 litre air cooled flat four), its specced to run the first 50 hours on straight mineral oil with no additives and to be thrashed rather than lugged to get the rings to bed in and not glaze the bores, its 1930s technology
Modern stuff hardly needs running in at all, modern oils, nikasil plated bores and finer tolerances in manufacture pretty much delivers a ready to use product
the car as done 100s and thousands of numerous miles before its placed in its body
You what?