Re: Info on '82 LTDs
You can run Mustang shorty headers and a Mustang H-pipe. I'd recommend a stainless steel piece, if you can. I went with aluminized steel a year and a half ago and I'm already replacing everything (and I don't even see any road salt or anything of the sort) because it's rotting through. Find some good stainless steel mufflers (get a baffled design, NOT straight-through) and bring it all to a muffler shop, to have them install everything into place. Be sure they put flanges to match the H-pipe and don't weld the H-pipe into place (dropping the H will come into handy if you need to drop teh transmission for anything).
If you can, run ALL 2.25" equipment. 2.25" collectors on the headers (stock Mustang headers are a great option and can be had for cheap, if not free), 2.25" inlet/outlet on catalytic converters, and 2.25" inlet/outlet on the mufflers. That'll help build the low-end torque you'll need to get that beast moving. I went with 2.5" and lost out on a lot of power. By the time the bigger exhaust would have been able to make a difference, I was already beyond the power band of the motor.
Good luck and keep us posted on that thing!!