This billet aluminum housing for Evo 8/9 Idle Air Control motors is the perfect solution for that custom manifold you are looking at. This flange features a flat bottom so it can be custom fit to your liking as well as a 3/8" NPT fitting provision for a wide variety of fitting choices.  
 
We have also started to experiment with RB26's on AEM Infinity which allows us to utilize this flange and Evo IAC instead of the bulky factory system.