A/C compressor differences

In 1969 the parts book lists different part numbers for the A/C compressors, my Coronet 500 has a different part number than Chrysler 300, anybody know what the differences are to require different part numbers? Isn't a compressor just a compressor?

I only know that a small block compressor is different than a big block. The BB has a bigger sump on the bottom.
Ron

From my personal observations the sump is the only difference in bare compressors.

Some have a through bolt above the crank. The one with a hole is from a `69 A-body 340, the one without is from a `75 B-body 400.