flange dimensions. The Garrett T3 turbine housings for the GT30 series turbos are noteably longer from the CL of the turbine to the flange. Because of this, I think it would be very difficult to make a manifold that could be machined for one or the other.
Regardless, whoever does it will have to make downpipes for the application because if they don't they'll be missing out on the bolt-on market.