The Buick LeSabres, Wildcat, Electras, and Riveras of 1964 used a Frigidaire A6 Compressor. This robust compressor, over-engineered for its time, was later used in transit busses and farm equipment because it had a cooling capacity of 12,000 BTU. The average $100 (2019 dollars) house window air conditioner has a capacity of 5,000 BTU. The compressor came off my parts car, as the factory air conditioning had been removed from my car. I'm unaware of the actual operating condition of the compressor. It spins freely, but I have not yet charged the system. I was originally going to leave it looking as it did, but after detailing out the whole engine bay, it would have been quite visible being mounted at the top left of the engine. Below is the condition of the compressor when the project started.

While I was able to get reproduction stickers for the warnings and nameplate, I haven't run across the stamp that says "OK FINAL TEST BUICK". I actually covered the stamping in blue painters tape and then painted over the whole lot. Should I wish to reproduce it in the future, or prove the compressors providence, I can pull the tape off.

After much sanding and coats of Eastwood paint, below, the compressor clutch is looking drastically better.

Because I knew replacing the factory labels would be key to this cosmetic restoration, I layed a piece of paper on the compressor before hand and traced where each sticker was located. The stickers were not applied to the unit squarely nor straight, so this template let me put them in place exactly where they were removed.

The serial number of the compressor is punched in 1/8 high characters. I didn't do a search for factory perfect punches, I used what was available locally. Because of the size of these punches, and the character spacing that would result, I couldn't punch the characters in one shot like the factory. Doing that would have resulted in the characters overruning the box. 

The decals are Jim Osborne reproductions, sourced through https://bestoffercounts.com. The reproduction Fridgidaire decal is square whereas my factory original had rounded corners, so I adjusted it with a pair of scissors.

Before the characters were stamped I used a black magic marker to fill the box.

After the characters were stamped I used an Alcohol prep pad to remove the non-depressed ink resulting in visible letters. It isn't perfect, but this isn't a Concours restoration either.

Finished product.