The USDM has a DCCD in addition to a front and rear diff, when you apply the brakes the DCCD unlocks so ABS can work.
no ABS JDM STI = 3 LSDs with no DCCD
JDM STI W/ABS = DCCD+F/R diff or Front open diff W/Center and rear LSD
For your transmission identifying pleasure
The v8 will easily make 400 WHP GT30 power levels, unless you are going farther the factory motor is plenty. A bad tune will break any motor so we are talking safe well tuned power here.