The 250's suffer from poor intake ports on the heads limiting air flow, and ultimately power. The engines will spin to about 9000 RPM which will get you lots of upper end power, however not much torque where you need it. Not much except a lump head conversion will help airflow for a naturally aspirated engine, however throw a turbo or supercharger on it and you can get a whole lot of power.
Although a 268 Comp Cam, Clifford Intake, Exhaust Header and Holley 390 would be the way I would go.
