The two manifold-mounting bolt holes in the rear are the most unpleasant to get to, I am not sure how it would be with M10 hardware. If using an aftermarket manifold where all the manifold studs can be accessed from the top, I would just tap the holes on the turbine housings for M10 and use bolts/studs to fasten the turbo from the top, similar to how RB26 turbos are.
As for hardware, I am using ARP, though I do not intend to any racing, I am sure inconel would be best.