Thank you for the kudos my dear friend. Everything in your article is correct except for a few small details. As long as you use all factory installed a/c component for 1979 620, you only have to purchase a York to Sanden adapter to mount directly in place of the York compressor original mount location. You can re drill holes on adapter plate to line up Sanden compressor with pulley with original pulley tensioner that covers the timing belt cover. As long as you have complete system intact, all someone has to do is update York compressor to a Sanden compressor. I completely dissembled my entire system and flushed with a/c flush (remove expansion valve
prior) (Spray system available from Autozone free loaner tool program). Replaced the expansion valve and receiver drier with new units which are dirt cheap. I used original flare fittings a/c hoses because I felt condition of hoses were decent. Before assembling everything back together, I lubricated all flare joints with a product called (Refrigeration Technologies RT201B Nylog Gasket/Thread Sealant) this helps seal all joints to keep refrigerant in system. I then used a vacuum pump to remove the air and moisture from the refrigerant system (vacuum pump available for free from Autozone free loaner tool program). All sanden pumps are r12 or r134 compatable, just depends which type of oil you use. I used AC Delco 15-117 air conditioning system mineral oil because I wanted to keep r12 system. System recommends 8 oz. mineral oil capacity for Datsun factory installed system. I then filled system to recommended r12 capacity of 2# of r12. My system had the 8 blade fan, my mistake is I did not replace the water pump with a new clutch. As you stated it is crucial. As far as being ugly, I disagree, the ugliness probably from my clustered engine bay..LOL. It is all original placement from factory with only addition of upgraded Sanden compressor mounted in original pasenger side location. The bracket is supported with the two mount bolts that pivots the compressor adapter plate in towards the engine keeping it tight from movement as the tensioner pulley tighten the belt. As for coldness of air coming from vents, my system blows average 29 degrees at the vents. Seeker, when you felt it I had just started my truck before leaving Eagle Rock (Reason why I chose to stay with R12). I must also give you kudos on a well informed wealth of info on a/c. As far as I am concerned, I like the the system, it is old but works for our trucks.
Seeker great info
Parts used ordered on Amazon:
Four seasons expansion valve part # 38608
Refrigeration Technologies RT201B Nylog Gasket/Thread Sealant
Johnsen's 6545-6 A/C Flush- 32 oz.
York to Sanden adaptor mount purchased on Ebay https://www.ebay.com/itm/YORK-TECUMSEH-TO-SANDEN-COMPRESSOR-BRACKET-KIT-SD709-SD5H14-SD7H15/282598743519?epid=1717932436&hash=item41cc329ddf:g:Rr8AAOSwJS5ZhMyo:rk:4:pf:0
If I can assist anyone in the Los Angeles area, PM me.