for 96-up 4.3, 5.0, and 5.7L Vortec engines you dont need that. if you look at your belt routing label, you will notice the "non A/C" routing is also shown.
there is a hole on the A/C P/S bracket for the extra "non A/C" routing pulley that the factory uses. and you dont have to remove the compressor. it will require a shorter belt though.
but you really dont even need either this exra idler pulley, or the one on the alt. bracket, thats just above the water pump, if you are bypassing the A/C...
if you have stock pulleys, you can get an 850K6 belt, and route it straight from the alt. to the P/S pulley.
here is a link to a thread on s10forum with pics., that shows this.
http://www.s10forum.com/forum/showthread.php?t=217704