No I haven't actually.Yeah i guess so mate. Have you had a look at the king brown systems? Iv heard good things about them. Probably a bit pricey though
I was looking at the dea one for obviously cheap as hell. I went with redback one.
http://www.redbackexhausts.com.au/images/docs/Redback_Media/4WD Action BUYERS GUIDE redback 4.pdf
Why don't you see what your local exhaust shop will quote you for a custom make one?