love the idea, a little worried about the execution.
These mods would not pass certification here in New Zealand, and if you look at any galant 4wd chassis, even with 3" exhaust, they dont run in the tunnell, your best bet would be to run it straight down the right hand side of the car, from the turbo back and have it exit on the other side of the bumper, like an evo, relativly straight.
Also that diff wont last 5 minutes, get that out of there in favour for a LSD inside a STR wagon rear casing.