Commo, what do you want? You dont want corners, you dont like tunes, and you dont want to get all the little things that improve performance.
But you want an underdriven pully? I already discussed it with a fella from work(He's been a mechanic for 30+ years and rebuilds old cars for performance), he made a point that if you get 20% back from the power lost to auxiliary's, you may get a couple extra kw's. Which is basically nothing, compared to how much they cost, and having everything underdriven(Including WaterPump).
Stick to the basics, Intake, Exhaust, Fuel, Timing. After all the little tweaks are done, get a tune, it does make a difference because every stock car is programmed for comfort and fuel economy. If you want more than a 40kw gain, get a supercharger or get a new car.