One muffler I've heard works well is the Aero AT2525XL.
If you're interested in headers, you'll need to go custom.
http://www.ebay.com.au/sch/sis.html?_nkw=EXTRACTORS+HEADERS+V6+3+5+MITSUBISHI+PAJERO+6G74+6G75+
...there are headers. You may just have to pay a few bucks extra for shipping. It would be cheaper than custom headers.
PS, here's some ideas...
http://www.youtube.com/results?sear...221.1102.4j5j1.10.0...0.0...1ac.1.3HKed5xAAhc