I'm one of the several guys on this board who's performed the installation of the Kooks headers and complete exhaust package themselves. The Kooks system is now a complete bolt-on kit. If you get the complete kit like I did which includes the 18" straight-thru design Magnaflow mufflers, there's no welding to be done to install it. I didn't need any welding done at all, but the only potential weld that you'll need is to connect the back end of the passenger side muffler to the tailpipe because of the difficult bend on that side. But even if you run into that, the entire Kooks package can be installed first, and then you would simply need to drive the car to the local muffler shop to get that one weld performed. No big deal or expense.
Like most long tube headers, the Kooks headers were challenging to install. But it's "do-able" if you have tools, motivation, and some patience. Count on 2 or 3 days to get the entire exhaust system including the headers completed. If you get it all done in one day then I'd consider you superman. but it was well worth it for me. Remember one thing, Kooks is the only place that makes standard conventional headers for the Marauder, Kooks does NOTHING else but exhaust(that's their specialty and has been for years), and Kooks is a well known and well respected header manufacture throughout the entire country in racing circles. Kooks mandrel bends their own pipes, they have all the equipment right there.
I talked to a guy I know from California(I'm from Connecticut) and this guy races a 9 second car. As soon as I mentioned Kooks to ask him about them and their product, he immediately recommended them and indicated that they're well known in his circle of racing and abroad. That alone impressed me.
If you decide to perform the installation yourself, send me a PM, and I'll go into more detail about what has to be done.