Theres a few off the shelf kits availiable for it.... but they arent cheap.
Aussie Exhausts in Albion, Brisbane do a complete downpipe, b-pipe and rear muffler.
The rear muffler on the turbo sw20s arent too restrictive, but the main restriction is the cat/downpipe with its nasty 90 degree bends.
For my system I imported a 3" inlet N1 muffler from the US, which was around $160 landed, bought a flexi from Tyco $50 (muffler shops will try and rip you 3 times that) Aussie downpipe around $500 and 3" custom mandrel bent piping and flange onto the downpipe $300