Sometime around the 2004 model year (which is when the Series 3's came out), GM switched to a scroll type A/C compressor which direct mounts to the 3800 block (no other brackets needed). These scroll type compressors also used different A/C line hookups than the earlier compressors did.
You can use an earlier type A/C compressor on a Series 3 (or Series 2 engine that came with the newer scroll type compressor) if you get the compressor mounting brackets and lines to get it mounted and hooked up to your car. The mounting points on the engine block are no different. This means you could also use the new scroll type A/C compressor on the older engines if you wanted to.
OVERKILL IS UNDERRATED
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