Ok guys I can give you some insight on specs, etc.
ATP do not make a stage 1 or stage 3 high flow. They do, however make a stage 3. Don't ask me why it's like that, I don't know!
Basically, the housings (that you supply) are machined out to fit much larger compressor and exhaust wheels. The core is a new T3 item, oil and water cooled. It is a standard bush bearing core. The exhaust and compressor wheels are found in Sierra Cosworths. When 'highflowed' to these specs, they are commonly known as Sierra-Sierra turbos. They are rated at 450hp.
You will be looking at around $1495 to get this done.
Speak to Kyp Matheou.
9569 4764
ATP
1198 Dandenong Road
Murrumbeena 3163
I'm guessing it's not a bad turbo to have, and I looked into them when I was looking at getting mine high flowed. I bit the bullet and bought a GCG highflow instead. The ball bearing new garret core of those things (basically the same specs, exhaust, comp wheels, etc) was too much of a benefit for my application. They aren't cheap though, $1900....