* Camshaft: The camshaft profile significantly impacts horsepower. A mild cam will produce different results than a performance cam. This is arguably the biggest variable missing from your description.
* Exhaust System: The exhaust system's design and flow characteristics dramatically affect power output. Restrictive exhaust severely limits performance.
* Ignition System: The ignition timing and overall quality of the ignition system plays a crucial role.
* Intake Manifold: The intake manifold's design affects airflow to the cylinders.
* Compression Ratio: While you've specified 10:1 pistons, the actual compression ratio achieved depends on head gasket thickness, milling of the heads, and piston-to-head clearance. A true 10:1 ratio is not guaranteed.
* Internal Engine Condition: The condition of the internal components like rings, bearings, and valvetrain will impact horsepower.
* Tuning: Proper carburetor jetting, ignition timing, and overall engine tuning are critical for maximizing power.
Estimate:
Given the components you've described (454, 10:1 forged pistons, .030 overbore, 1968 325hp heads, 750 Holley), and *assuming* a reasonably efficient exhaust and a moderately aggressive camshaft, you might realistically expect somewhere in the 450-500 horsepower range at the crank. However, this is a rough estimate. It could be significantly higher or lower depending on the factors listed above.
To get a more accurate prediction, you'd need to specify the camshaft details and exhaust system. Even then, dyno testing would be the only way to know the exact horsepower output of the specific engine.
