Here's my DIY job...
First get a rear header from a breker that has already been cut for a slip-on. This way you can keep the original in one piece...
Then get some bends from an exhaust component manufacturer. These are mandrel bent stainless. And make a stainless steel adapter plate to suit the carbon can you picked up at an auction (new) for about 20 quid...
Find your local tech college welding instructor (guru and artist with TIG) who welds it all up for you...
Make a rear peg spacer from 25mm square alloy tube, giving you enough room to have the new header pipe go behing the peg.
Total cost? Under 100 quid...