In my humble opinion, not that it seems to count for much, I don’t think that you should try to modify and fit this muffler to your bike. It is something that I, personally, would never contemplate doing.
http://obtrailriders.com/index.php?option=com_kunena&Itemid=56&func=view&catid=18&id=3118
If I were ever to do such a modification, I would probably acquire the mid pipe of the standard setup, as it already has the designed bends and mounting points. It is just a simple case of attaching the muffler to the mid pipe and making sure that it is not twisted. That would look dumb.
My advice, should you decide to listen to it or not, is to spend huge amounts of money on an aftermarket system, which at the end of the day, probably will make fark all difference to the performance of the motorcycle in question. The only benefit would maybe be in the area of weight saving. If this is really an issue, just have have a big dump before you ride. This is worth a kilo or two.
Don’t ask me about appropriate jetting to suit, as I know nothing.
All the best. I will go now go back into my shell.