Cadillac only A6 compressor?

[Pghcc2006]

Good evening gentlemen

I am looking to buy one of these three compressors:

1.) https://www.originalair.com/a6-gm-5-single-groove-compressor

2.) https://www.oldairproducts.com/product/21-3221-compressor?gfid=p117742-c126082

3.) https://www.oldairproducts.com/product/21-2215-10-compressor?gfid=p117738-c124623

Number 2 appears to be a Cadillac compressor? Not sure what the difference is as the company did not answer my question. Would it apply to my 76 Fleetwood or an older model?

Also what was the clutch diameter for these cars? There appears to be a 5 and a 5 1/4 on one?

Sorry for all the questions but I'm spending a lot of money rebuilding/replacing my A/C system and I want to do it right.

["Cadillac Kid" Greg Surfas 15364]

According to what is shown here, the first two compressors are both rebuilt and do not have any differences. The third at over $600 seems to be a new compressor, but does not specifically say so.
The 5" pulley will turn slightly faster, providing a bit more cooling at low speeds.
Greg Surfas

[fishnjim]

If you can get all the part numbers off your A6, it would make matching it much easier. 
Not unusual to find two different for the same year.  Sometimes they change parts when the old one run out or different optioned vehicle or substitute when the NOS stock depletes.   It should be in the part list for your year car. 
I don't think the A6 was Cadillac specific.  Most all the big GM would.   

[TJ Hopland]

Didn't one say its got a super heat port and the other one said super heat switch?  Maybe one includes the switch and the other doesn't?

["Cadillac Kid" Greg Surfas 15364]

All of them just have the port, meaning they had rear heads for 1979 and later. There is no mention on any of these about having high pressure relief s which I  believe were on compressors after 1973.
Greg Surfas