* Compression Ratio: The stated components don't specify the compression ratio. This is a major factor influencing power output.
* Intake Manifold: The type of intake manifold (e.g., Edelbrock Performer, Weiand Stealth) significantly impacts airflow and power.
* Carburetor: The size and type of carburetor (e.g., Holley, Quick Fuel) also affects the engine's breathing and power.
* Exhaust System: Headers vs. factory manifolds, and the diameter and length of the exhaust system, all affect back pressure and horsepower.
* Ignition System: The quality of the ignition system (coil, wires, distributor) affects combustion efficiency.
* Internal Engine Condition: The condition of the pistons, rings, bearings, etc., will significantly impact the engine's ability to produce power.
* Tuning: Proper tuning (carburetion, ignition timing) is critical to maximizing horsepower.
A 455 with XE274H cam, bored .060 over, and 6X-4 heads *could* produce anywhere from 350 to 500 horsepower, depending on the factors listed above. A well-built and meticulously tuned engine on the higher end of this range is possible, while a poorly built or tuned engine might fall toward the lower end. To get a more precise estimate, you'd need to provide details on the other components and the quality of the build.
