The truck had headers on it when I bought it. I didn't really like the headers, so when I put the L31 in it I installed 2.5" rams horns. Currently I have the old exhaust from the headers back. I just welded up some 2.5" tube that I bought at Speedway Motors (see this link:
http://www.67-72chevytrucks.com/vboa...d.php?t=817921), but I plan to replace the entire exhaust this summer. The existing exhaust is 2.25" with some really crappy bends and really crappy turbo mufflers. They are dual exhausts exiting behind the rear wheels.
The wires I used are for a 76 Corvette with HEI. I ran them under the rams horns. One of them is a little tight, but it works. I used Taylor 8mm wires, but any wires for that application should work. The other option is to buy cut-to-fit wires.