Exhaust question
 

The Raptor comes stock with a 411-hp, 434-lb-ft V8, the 475 upgrade from Hennessey boosts output 64 hp, adds an HPE air induction system, stainless steel long-tube headers and a high-flow catalytic converter. Hennessey changes the engine programming with a handheld programmer. The long-tube headers probably make the most significant contribution.

My guess would be outsourced based on all the models of vehicles they offer packages for. Bottom line is almost any brand of stainless steel headers are going to change the sound of your truck with an added benefit of more HP and torque! Altering the airflow out of the engine with headers and high flow cats may require altering the intake with higher volume or at least changing the tune in the ECU to handle the difference. If you just want more noise save your money and just change the muffler. Ford actually does a pretty good job on the intake and exhaust flow on the 5.0. Lots of good info from the Mustang world on this upgrade too.

Long tube headers tend to increase low end torque since they provide higher exhaust inertia and are more efficient at scavenging at low RPMs, but the additional friction of longer headers can rob horsepower at higher RPMs, so its a trade-off.

Yeah, that's kind of a generality since tube diameter is just as important as the length of the tube. A well engineered header will balance tube length and flow velocity to optimize both torque and horsepower across the band, but in general a longer tube will offer better gains in torque than a shorter one.