No eBay APP ID and/or Cert ID defined in Kunena configurationi would do as you have done and find an exhaust i like .then study it as well as possible and then order some nice components and build what i wanted.
it could be done cheaper by sourcing a bunch of different bends and collectors from other header .but i can tell you from experience that once you get it build after dealing with all the old rust ,carbon build up and general corrosion.that you will be less frustrated and have a better end result if you start with the nicest stuff you can get.
www.coneeng.com/motorcycle_components.html
or just give these folks your money and buy one of these.
japan.webike.net/products/22623690.html
webike usually has some more affordable options(around the 400$ish zone)for headers and is good to buy from.communication lacks a lil but they've always come through for me.
i've wanted to purchase one of these
and some pieces from cone eng. and try to build my own Kerker replica.but i got to many projects in line for awhile.
thats my .02 fwiw,
can't wait to see what you do.
keep us posted,
leon