Great right up as usual Steve. I must have seen this before.
I did the exact same process 4 years ago before I decided to rebuild my coupe. The only difference is I had a bracket for the compressor from a 86-88 535 and had to do some belt testing to get one the correct length ( a local old time parts store let me take belts to try and then buy the one I needed)
The other difference was that I used R-134. I was very concerned about R-12 and it's future supply. I also had great success with my 88 M5 and 134. It really surprised me how cold it can get.
Luckily it cycles well and does not freeze up.
Like Pickman says increased capacity of the condenser helps a lot. Unfortunately we can't make the evaporator any bigger which is where we could get huge gains in cooling.
I also replaced the expansion valve as I wasn't going to go through all this and have dirt in the valve and have it not work. Had to take the all the center console and heater out to do that. PIA for a $50 expansion valve. Available at the same place you get the upgrade condenser.
One thing I have always wondered is if size of the orifice in the expansion valve should be different for R-12 versus R-134. I ask Rob Siegel when he wrote his book about AC systems and he never answered me. I'm not an engineer.
BTW Rob's book is a great resource for everything you didn't want to know about auto AC.
Insert shameful plug here.
https://www.amazon.com/Just-Needs-Recharge-Mechanic-Conditioning/dp/0998950718
I also used the original fan and kept the circuit the same so the fan turns on when you turn on the compressor. Simple and seems to work well.
After I rebuilt my AC system I could get 34-36 degrees at the grill with an auto AC stem thermometer. I have had it freeze up a couple times on long trips like when I drove to Colorado and back in 2014. I also did this same procedure to an all original 74 3.0 CS that belongs to a friend. Parts and labor was about $4000. It a very tedious job.
One thing I wish I had done is convert all the connections to o-rings and get rid of the flare fittings and copper gaskets. Luckily I have an AC shop that pulls the vacuum for me and tests the integrity of the system before I waste a bunch of Freon. I even taken tools and loosened a fitting or two and put in another copper gasket to get it to seal. If you use some of the same oil that is in your compressor on the cooper gaskets it lets them slide around a little as you tighten the fitting hopefully getting a complete leak tight seal.
Gary