I have a 1974 Dodge Charger SE with the factory dual exhaust that needs work. It appears the gasket is leaking between the pipe and right manifold, but can see it's been replaced before. Also, tail pipe is bent and hitting on left side above axle. Both pipes have been butchered by current turbo mufflers and have 3 different sizes (2 1/4", 2 1/2" and 3"). Just going to remove it all and replace it. The engine is the 400 HP. It now has Edelbrock E-Street aluminum heads, Performer intake and Performer Carb. Auto tranny has a B&M shift kit according to previous owner. It has a mild aftermarket cam, but I don't know what since it was replaced before I bought car. Car runs fine and is a street driver built to perform between idle and 5500 rpm. When I bought the car, there was a brand new set of Hedman headers (78030) in the trunk he planned on installing but never did. I have decided on going with a TTI 2.5" exhaust with H-pipe. The current manifolds are the 74 (only) HP manifolds 3751068 and 3751071, which do not have a heat riser in them. I am far from an exhaust tuning expert. Question is should I replace the HP manifolds with the headers, since I already have them? Or keep the HP manifolds on since I already have them? I don't plan on changing much with engine and am currently guessing it has 400 HP or less. It will be a daily summer street driver so no interest in building a high HP race car out of it. Thanks in advance for your input.