Steve
I purchased my magnaflow cats from tuffcarparts.com.au Speak to Justin, he'll look after you with pricing and fast dispatch. There ebay store prices are a little dearer.
Ebay is worthwhile to check both round & oval shaped cats, as the oval ones may have a little more ground clearance than the round ones I bought.

- 2.5" Cat round
- 2.5 Cat round.JPG (54.2 KiB) Viewed 2407 times
The cats on welded to the rear extractor flange supplied by Raptor with about a 3" pipe extension from front cat outlet to the flange. This is done to keep the front sensors in the factory location. ie same distance back from engine exhaust manifold. Custom 2 into 1 collector pipe with no 3rd cat was built to link from the rear of new cats to the front of the factory mid pipe flex joint. Ive kept the mid pipe with resonater and rear y-pipe factory at this stage. The thinking behind keeping these
sections stock is to retain good low end torque. This seems to have worked well.
Tcp quads bolt straight up to the stock y-pipe flange.
Grant