Al, It depends on the combination of camshaft, carburation, ignition, etc. Not just the heads. The 351C is well known for making horsepower at high rpm, not for making low end torque. Port plates for the huge ports will help some or the Australian 2V heads will be even better if you want torque. Floating the valves at 5,000 rpm could be the camshaft, carb , ignition combo you have. I would call some of the people who are in the pantera business. Do you belong to Pantera International? If not, you should join. It has helped me for 17 years. I hope this helps
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