I found headers for 4.2 liter engines at truckperformance.com. they are JBA headers. Nickel chrome for $370, silver for $525, and titianium for the same. don't know if this is any help to any one but the only other ones i ever found were $489 to close to $700. thought it might help any one looking for a little more out of them 6's. Whioch by the way i had my tool box about 300 to 400 lbs and 500lbs of sand bags and went right up the mountains in central PA without droping speed.

 

I just found another at shmotorsport.com for $308. performancecombos.com also has these headers for about the same price as truck performance. they also have some cheap Cats and mufflers too.

 

I'm not absolutly sure, you should check with other people, but the 4.2's supposedly need a lot of back pressure to work right and it may decrease it when you put the headers on. I tried putting on an exhaust cut-out a while back and I lost all of my low-end torque. The flo-pro dual exhaust I have works fine though. Just putting my 2, maybe 1 cent in.

https://www.f150online.com/galleries...TOKEN=37026799

 

Ive heard the same. Someone at fordf150.net said that they put some gibsons on i believe and they lost alot of power. Look around and see if you can find talleywacker, he seems to know quite a bit about the 4.2 and how to beef it up.