I run the GT2X conversion as many of you know, for 7 months it has had some serious stick (not on a track though) and so far no cracks or problems.
As for the fitting issues with the ATP Manifold i have major problems, then when the gasket blew it had to come off again, but it wouldn't budge due to the bolts touching the casting they just rounded off.
I removed the cylinder head and had to grind the nuts off. By this time i was sick, so i called my dad so he could take a look. (clever bloke). The fix was quite simple.
The stud holes which are close to the casting were elongated so that we could get M8 (6mm) allen headed bolts in the complete top row.
So next time it has to come off, it will be a piece of cake.
I would not be using the standard manifold for high power applications. no way!