340 exhaust system

I am currently installing a 340 in a 67 Dart. I was wondering if anyone has any information on what type of header to run. I am looking at at the TTI ceramic coated polished ones. The car rides really low and currently bottoms out with the Hooker full length headers I was using on the old 318. Thinking about running the shorty type but TTI says they will restrict the HP. I have a 340 with aluminum heads, factory six pack running a Lunati roller cam. Engine builder says based on the specs motor should be between 415-425 HP. TTI says 450hp max with the shorty headers. Anyone know how well the TTI headers fit and if they will save ride height like TTI claims. They are ridiculously expensive. If not any suggestions on what ones to buy. Car is still using a factory torsion bar suspension.