I recall we made a 3" stainless intake from the airbox and to the turbo for my VQ25det way back when. I designed it so that the path was as straight as possible. Scott made the top and bottom section out of stainless (lobster cut which allowed for tiny adjustments, then smooth out the internal walls) and we clocked and connected each to the OEM MAF assembly with cut down silicone joiners to keep the continuity of the internal wall.
Unfortunately I can't supply photos as Photobucket now have them behind a ludicrous paywall.
There was very, very space between the rocker cover, exhaust manifold and the intake, but it was thoroughly wrapped top to bottom so heat was not a massive concern. Just make sure that your air flow sensor is on a straight part of the intake. If it is on a bend, it won't register the airflow properly and will stall.