Originally Posted by phunk

Some custom 3.5" tubing to the inlets should help a bit. Custom 2.5" outlets just to get from the turbo the front of the motor and then go up. Custom set of hybrid turbos made up to fit the FI manifolds. Lately the GTR community is popularly using the stock turbos as a starting point for all the way up to 1100-1200whp... for example: https://www.boostlogic.com/product/1050x-turbo-kit/

Given, they are really only carrying over the manifold with turbine housing. You can see where they weld to the turbine housing area a bit to get an entirely other turbo to bolt up. No doubt that inside the housing is machined out to fit a larger wheel.

Id say that starting with the FI turbo kit has a leg up on starting with the tiny stock GTR manifolds and turbine housings. I think those BL turbos making 1200 linked above are based on the newer Garrett G-Series, but I havent investigated it