Here is my problem, I have a 1976 Eliminator Daycruiser that is still the the way that Bob Leach built it in 76. I can get 70 mph out of it at 5500 rpm with a legend 12JG pump turning an AB cut impeller. I would like to get 80-90 mph out of it. I have Aluminum Glenwood logs and riser for exhaust on it now. The engine is a Guardian high output 454 with rectangular port heads I have to free up the exhaust path in order to get any gains from a cam change or intake change. What exhaust system will fit under the engine cover? Emi Thunder, Dana flow torque, CMI, Lightning?