With just the Eurocharged custom dyno tune only output rises to 358 wheel horsepower and 269 pound-feet of torque at the wheels. With the addition of an underdrive pulley this grows to 369.4 wheel horsepower and 273 pound-feet of torque.
The tune only gains are an incredibly impressive 39 wheel horsepower and 25.4 pound-feet of torque at the wheels. That is flat out gigantic on the S65 V8 tune only. The total increase with the underdrive pulley plus tune over the baseline is 52.4 wheel horsepower and 29.4 pound-feet of torque. The 369.4 wheel horsepower figure would be close to the ~400 wheel horsepower range on a Dynojet.
Keep in mind this is likely 93 octane fuel. What this goes to show though is the difference between a custom Dyno tune and an off the shelf file. There is also different pricing for both but these are some of the strongest tune only S65 V8 gains seen.