It's all in the ECU which will control things like the turbo boost and injector flow, amongst other things.
Problem is that the ECU can be coded to only work on a specific model, so putting an ECU out of an FE into a FG may not work, unless you can get some assistance from someone with a genuine MUT-III reprogramming tool.
I looked into this a while back when researching options for additional power in my truck. In the end I put doing an ECU swap into the too hard basket, choosing to go with a Steinbauer power chip instead.
Would be very interested in knowing the outcome if anyone is willing to attempt an ECU swap.