Re: laws on extractors
It is possible to fit extractors and maintain a catalytic.
As suggested Falcon cats do flow well, but there are better ones on the market.
My suggestion is to find a performance exhaust centre near you and sound them out. The really good ones won't hesitate to recomend a set-up to suit what you want and stay legal!....a really good one will even quote the part numbers..meaning they have done it before!
I have found Unique Exhausts in Boronia (Melbourne) to be very good, but i don't know where your from.
All i can say is to stay away from run of the mill joints like Midas and Mr Muffler, as they are NOT interested in out of the norm applications.