You need to break in the engine how you are going to run it during normal use.

You dont break in a F-1 engine in a airplane then trow it in your F-1 car and go race lemans.

break it in mounted in the car like it was intended. If you break it in with a constant load then throw it in a car with a changing load all the time then you are adding a different load and heat set in the engine and it wont last as long. Running with a constant load with a propeller or anything else you will be running the engine with more oil and more fuel to run for a few minutes and WOT. In a car you are running less oil and a leaner mixture to get that accel that is needed in a car. Because a car engine is only WOT for 10-15 seconds or less it builds a different heat set in the piston and sleeve. So they will have different wear patterens in the engine if ran differently.

I know everyone likes to tinker and all. Its you engine do how you like but i dont think you will get the results your looking for.