Yes the 30 revs is because wind turbines can be made to give high torque at low speed, the higher the number of blades on a turbine the higher the torque and the lower the speed.
I'm not sure what you are doing exactly, if you want to drive the wind gen permanently from the engine, ie not use it as a wind gen anymore then if the wind gen has a gearbox to increase the speed to the alternator/dynamo remove it and drive it direct from the engine, if the alty/dynamo rotates at the same speed as the blades then you'll need a reduction box for the engine, there are various ways to do this depending on your skill / budget, you could get hold of a cheap geared motor, remove the motor machine a pulley and use its gearbox, or use a vehicle gearbox then you'll have changing gears, or even for a beer budget repurpose some pushbike gearing parts, 5kw might be too much for bicycle stuff though.