Welcome. Had a 76 Sahara with AC and a sunroof that was my daily back in the day. Had the time of my life in that car though it barely kept you cool in hot, humid DC summers. Happy you finally realized your obsession with your 74.
Fast forward, I have Behr AC in my 74tii. When I bought the car last March the PO said she never ran the AC in the 13 years she owned the car. I finally got around to getting the system recharged and immediately ran into problems -- my mechanic said there was a short in the system that was draining the battery. The local radiator/AC shop was extremely hesitant to get into the system beyond the initial recharge. They didn't want to touch the dash (they said they'd need to remove it) and I didn't want them touching anything if they were unsure of what they were doing. I eventually found a place that will work on the AC, the car goes in next month. I am in your same spot, do I go the route of saving the existing AC or putting in a modern system. Good luck whichever way you decide to go. Cheers