That looks like fun!
I spent the morning helping a buddy with his 87 911 A/C upgrade. He was nervous about the sensor placement into the evaporator. It was a pretty easy project. Then he took me to breakfast as "payment" for my help. I told him to swing by once the system is buttoned up, and we can pull a vacuum, and charge with nitrogen and look for leaks, and help dry the hidden places water AKA ice can hide.
That is what he removed and is replacing. Everything is open to air, and the water likes to hide. We will pull a vacuum, purge with nitrogen, look for leaks wit the high tech soapy bubbles, fix any leaks, pull another vacuum, purge with nitrogen again to help capture any moisture. Then pull a vacuum to 90 microns or less if we can get there. Then he is hiring a professional to charge with 134.
Most all mechanics are used to working on cars with front engines, and AC components in the front with a few feet of hoses and all the components in the front. 27 feet of hoses, and lots of components front and back in out G body 911s is not the same. The average pro does not get enough of a vacuum.