Twins would take up far too much room. I like the dual BB GT35R idea better. Don't go too big though. With the turbo at the back of the vehicle you need to be able to spool it quickly. And providing 7psi to a 3.2l motor spinning @ 6000rpm isn't THAT big a task. And any plans for more than that will surely result in the eventual destruction of everything from your input shaft to your rear CV axles.

And I mentioned a large surface area but thin core air to air intercooler. That should provide the best cooling.
I'd like to find a way to mount it UNDER the car with vents to suck up the air running past it. That would give you more room to work with that cramming it in the nose.