HSV Extractor - cat modification

So I have bought a set of HSV extractors with aftermarket CATs which I won't use (the CATs that is). I now plan on welding in some VFii CATs instead to make them emissions compliant.
Basically the whole aftermarket CAT thing is only legal because it actually does convert "some" of the bad gasses, but no where near as good as factory CATs.
Anyway the pipe sizes are as follows:
1) HSV extractors have a 2 and 1/4 inch outlet (collector).
2) The Aftermarket CAT inlet pipe is 2.5"
3) The CAT outlet is 3" (which will match to my 3" CAT back).

But I don't trust the dimensions of the aftermarket CAT replacement. They don't line up or seem to finish in the same (mirrored) location, the drivers side CAT outlet flange seems to finish a couple of cm further towards the back of the car than the passenger side.. And it seems like the pipes they came with to fit up to a difillipo 3" have been modded so suite the dodgy CAT outlet flange location. I'll post some pictures to show what I mean.

I took some measurements to see if the CAT exit flange is actually in the correct location.. I measured 4 distances:
1) Passenger side rear of CAT inlet Flange to rear of CAT outlet flange on the outside flange bolt area = 31cm
2) Passenger side rear of CAT inlet Flange to rear of CAT outlet flange on the inside flange bolt area = 29cm
3) Driver side rear of CAT inlet Flange to rear of CAT outlet flange on the outside flange bolt area = 29cm
4) Driver side rear of CAT inlet Flange to rear of CAT outlet flange on the inside flange bolt area = 27.5cm

Can anyone confirm those dimensions are OK? I realise that just the two distances don't define where the flange is. But if they do match the factory parts then its a good sign.. Otherwise I might need to get some HSV CATs just to measure up bofore I swap in VFii CATs in place of the aftermarket CATs..

I should finally end up with a good Adr Euro emission compliant exhaust!
I'll get a tune too but not to turn off the Cat monitoring!

 

So I finally found some cheap VF headers and cats. They are actually of an LSA. I'm wondering if the cats are even cleaner (more platinum palladium etc) than the LS3 ones of the same size since the LSA will generate a bit more smog than an LS3..
Anyway they seem like they should be easy to mod to fit in place as can be seen from the pic with the HSV header on top of thr LSA combo.
The LSA combo also proved my suspicions about the aftermarket hi flow cats that I got on eBay. You can see that the rear flanges are not in the same orientation..
I'm now in the process of making a wooden jig to hold the header to head flange and the cat to catback flange so that I can get the new cat inlet and outlet pipes and flanges welded up.
BTW just a bit of info. The VFii cat cans are approx 15cm in diameter and 15cm in length (not including the inlet or outlet funnel).
Slowly getting there...

 

The VFii Holden and all the VF supercharged exhausts are a bolt up to any VE or VF cast manifold (even on a VE). Sometimes HSV had flared flanges and Holden had flat flanges though, but the CAT back exhaust location is basically the same. You can see from my latest pics above that the HSV (VE or VF) naturally aspirated headers have a different header to cat flange location. Its further rearward. So you can't bolt VFii Holden or VF supercharged HSV cats to VE/VF HAS naturally aspirated headers. They require shortening. And anyway I am enlarging the CAT inlet pipe and outlet pipe to 2.5" and 3" respectively.

I just found out that all VE and VF headers have 409 stainless pipes and mild steel flanges and the HSV supercharged cats are also 409 pipes and mild steel flanges. I'm not sure if the VFii pipes are 409 though..