Final answer:
The preferred method of running-in a rebuilt engine is to perform a dynamometer test run. This allows the engine to be put under controlled, varying loads and speeds, ensuring all components are properly broken in.
Step-by-step explanation:
The preferred method of running-in a rebuilt engine is a) Perform a dynamometer test run. In a dynamometer test run, the engine is securely mounted on a specialized machine called a dynamometer that simulates real-world driving conditions. This allows the engine to be put under controlled, varying loads and speeds, ensuring all components are properly broken in.