Ok boys, I´m done and quite happy with there result..
I gave up on the GT2-duct, just could not make it fit the way I wanted. Instead I flipped the radiator, grinded a bit om the metal frame holding the radiator so it won´t interfere with the side rad ducts. I found a "perfect" angle so I could reuse the original front duct.
I closed the outlet on the bottom with aluminium sheets. Well, here are the pics..
When flipping the radiator the OEM hoses do reach so no need to make it complicated and change hoses, I also learned that there is a valve for venting out the air after it is flipped (The blue one on pic-4).
Boxster S
Threaded Mode
