Many here diss the R4 reliability. I think Chevy owners have more problems since their R4 is mounted up high where it gets less oil. I had a Sanden compressor on my 1985 300D for several years, but then found I couldn't tighten the belt enough because the bracket had cracked (Rollguy's 1st design). I had a spare R4, so installed that and been fine for ~5 years and it gets to 110 F here. I didn't notice the Sanden doing any better, though I used the smallest H13 Sanden (for Honda Civics). Put it in my 1964 Plymouth Valiant since. I have bought new R4's for $50 on ebay, shopping in the winter (hint) and have another on the shelf.

The main concern with R4's is getting well oiled, since no sump. The best oil for any refrigerant is probably PAO68, which you can buy on ebay (or Duracool's "Oil Chill"). Consider using a HC refrigerant like Duracool or Envirosafe, since cools even better than R-12. Ignore the internet rants about "explosive" from gomers and writers who know nothing about combustion (I've taken graduate courses). Never a fire from HC refrigerant in many millions of cars using it for several decades, plus used in home refrigerators in Europe.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans