RE: WOT Break-in, step by step.
Most people dont have an engine stand so it isnt practical for them to run in using a prop. This is the main reason for doing it in the car but the principle is still there when using a prop you still running at WOT with a rich setting to limit rpm. So if you have and engine stand and prop this would be an easier way of running it in but the principle is still the same.
As for reasoning behind it Rody Roem using this method for breaking in all the Rb team engines. If it didnt work they wouldn't use it. I think they have a few championships to their name so his opinions are worth listening too. This is his direct quote when asked about the question.
"With the engine full-throttle, you are sure that the idle needle is not in front of the spraybar and so you are running the engine really on the setting of the main-needle and so are also sure the engine will run rich.
Also more fuel/air will go through the engine with full throttle so a better lubrification."