My dad is a car dealer so he bought his GTO from an auction wrecked. The best way to do a swap like the El Camino is to get a doner car for you have all the wiring and parts you need. If you are just going to do a motor swap then it might be cheaper just to buy LS1 motor and trans with the wiring.
I did a exhaust for a 2000 civic SI over the weekend.
He brought me a used muffler and resonator that I polished up.
I reused some of his old tubing to save him some money and just put the resonator in the middle. I did the rear section out of stainless and polished it all up.
I thought my dad and brother were crazy when they told me what they were going to do. I will have to say it turned out a lot better then I every thought it would. They said that they had at least 1,000+ man hours in it.
My dad and brother built the whole car, it took them about 6 months.
Here is a link to all of there pics.
http://s117.photobucket.com/albums/o57/dragsol/87%20ls1%20El%20Camino/
This is my dads car. It is a 1987 El Camino with a LS1 swap from a 2004 GTO in it and it also has all of the GTO dash and interior.
I started with the used Borla mufflers and tips that were cut off the GTOs exhaust and some stainless tubing from ACE stainless.
Than started to mock up...