Just My 2 cents but why in the world would you want to mess with that.... they dont make the much of a differece and they just make the accessories work poorly....AC does not work any good. power steering is weaker, and the alternator does not charge at low RPM.
And if you have a big amp your battery will just go dead all the time... underdrive pulleys are for race cars... not for vehicles that you are going to use every day..... spend your money somewhere else....
My friend had them on his Ricer and it just caused all those issues... and added like 2HP... WOW....
2007 RegCab STX 4.2L
Lowered 2-4 22" Boyd Wheels Foose Valance