Was told many years ago that if all the machine work is done correctly that there is no reason to "break in" the motor....minus of course the cam/lifters. This was by what was regarded as "the best" motor shop in NJ. During a trip to Island Dragway you would see there stickers on damn near every ones race car. Bill, the owner, would tell folks to break in the cam and then just drive the damn thing. He said that by babying it you were asking for trouble. Motor he did for me went over 400k miles without burning a drop....and I drove it on day one the way it was going to be driven its entire life.
Bought a sport bike right around the time he told me this. On the way home from the dealer hit redline several times. Rode the snot out of that bike....100k very hard miles never used a drop of oil. Same can be said for the bike I bought after that one.
How to builders "break in" a motor on a dyno? Let it come up to temperature then load the snot out of it....they do not spend a few hours varying the rpm & load.....
This topic has popped in the past. If memory serves me right someone mentioned that Caterpillar sells/sold a "break in dust" very similar to what is being discussed here. I would be concerned with some of this "magic dust" working its way into the bearings.....but perhaps I am just paranoid...