400hp n/a is near impossible without getting a built short blockfrom DSS or VT, port and polished heads, race cams with new valves&springs, aftermarket intake like reinhard, long tubes. Doing some port work on the intake and throttle body, bigger injectors, bigger fuel pump and probably still fall short of 400. 300-325 is a more obtainable goal unless you have bookoo money and then why would you have a gt and not an 03 cobra?
And just so you know, you're connecting rods are pretty weak. They're formed from powderize metal, so it doesn't take much more horsepower to cause them to fall apart. I don't mean to scare ya, but I would take care of the internals before you go buck wild crazy.