the idler pulley is fairly cheap compared to the compressor, normally around $40. it may depend on what year the engine is, whether or not you have a idler pulley. I think they used them all the way up to 99 but i'm not quite sure. but when they start to squeal, they normally do not last long and soon seize up and burn up the a/c belt. i've had that happen once before to me on my 91 LS and your setup is basically the same, belt wise.
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TR "Old Skool DA" Member #28