Just a suggestion. If you have the tools and talent to do the modifications you asked about, save yourself a lot of money and fab your own sidepipes. Believe me....it ain't that hard.
1. Cut your 4 header tubes where they go to into the collector and remove the collector/muffler/turnout.
2. Weld on a merge collector
http://www.summitracing.com/parts/HOK-11540HKR/ (or if you really want to do it right use
http://www.headermania.com/mm5/merch...=COLLECTORSPMC)
3.Get a muffler from
http://www.classicchambered.com/clas...cts.html#cobra (pick your flavor of sound level)
4. Cut off and reuse your old turnouts.
5. You will need to fab new supports.
6. Paint it and run it for a while to see if all is like you want it, then send it out for coating.
The trick is to keep everything straight and properly aligned. I cut, fitted, and tacked it all together with a TIG with it on the car. I then removed the sidepipes and completed the welds.
Rodger