Payu, if you want I can send these air horns out to you for testing. I believe they have the right dimensions for your itb, plus they're are curved at 45* degree so they wouldn't face directly at the fire wall.
Dimensions:
Length: 3" long side, 2.25" short side
Velocity Stack I.D. @ lip: 65mm
I.D. pass radius: 56mm
I.D. @ base: 51mm
The stack will accept 55-57mm O.D. tube. All you need is hose clamps.