I don't know if this is going to help, but it might add a little insight. Back when I finally had to replace the original R4 on my '84 305 (LG4), I encountered what I thought were some anomalies.
The original R4 compressors were later called 'R4 Heavy' when the newer, light weight clutch was in production. This is the original.
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I picked up one of the last GM/Delphi made compressors to replace it. It was hard to find, so I had the intention of changing the clutch from the serpentine pulley. I got what I thought to be the correct clutch (from a truck), also pictured with it.
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As it turns out, that clutch/pulley has the belt spaced positioned too far out from the compressor.
This is the clutch that I actually needed.
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Sorry the above picture is cut off. Seemed to be the only one I still have. The belts were aligned and the Gates belt (unknown #) fit down in the pulley well (same belt was on the R4 Heavy) Incidentally, the 'correct' clutch I used fits an '86 Old Cutlass Ciera with a 2.5 4 cylinder.
Between the janky spacers on the compressor mounts getting changed over the years (I bought mine new, so I knew it was still correct), GM selling the compressor design and tooling to Compressor Works, and possible other differences and errors getting into parts listings over 40 years, I'm not convinced the parts listings are always correct on these.
