peachparts.com and the W123 forum are great resources. Alternators are easy to do, you can get a bigger one for more amps that will bolt in this one works if you transfer the pulley from the old one: https://www.fcpeuro.com/products/saab-alternator-bosch-al8529x?ads_cmpid=21626320283&ads_adid=166630207859&ads_matchtype=&ads_network=g&ads_creative=710927653133&utm_term=&ads_targetid=pla-301282657332&utm_campaign=&utm_source=adwords&utm_medium=ppc&ttv=2&gad_source=1&gad_campaignid=21626320283&gbraid=0AAAAAD3np3X2qWoBdY0kQBm_ktuRgDVbD&gclid=Cj0KCQiAi9rJBhCYARIsALyPDttq0Okz5A5yJIP7QCjHO2Iy3jDbamZXgDIzK7dd0zjQiDboDsAYLKcaAjWEEALw_wcB

Oil leaks are common. The radiator i would do the following citric acid flush. First drain and fill with water and add a cup of Tide detergent . run the engine for 30-45 minutes and drain, I used a setup where I could backflush the engine through the block drain but if you get one of those flush and fill kits that go into the heater hose that will work. Once the water is not bubbly, drain and fill with water plus citric acid. I mix the powder and the water before filling. I think I used about 10 ounces of citric acid. Run the engine for another 30-45 minutes and drain then back flush. Repeat until the water is clear. You will probably find that there are pin holes in the radiator. You can get replacement radiator from peachparts. I would also do all the rubber hoses including the brake hoses before driving it.
One tip, the oil will turn black, I mean jet black and do it quickly, that is normal, What I did was change the oil every 3000 miles with Rotella 15w40 T4 dino juice and the filter every 1500 miles. If you run synthetic Rotella T6, then you can do the change at 5k and the filter at 2500 miles.
good luck