Also . . . depends on what state you're in . . . for instance, if you're down here in Florida, you'll definitely want A/C working, or any of the Southern States all the way to SoCal. I loved my ugly '76 240D, 4-spd "Pumpkin" because of it's simplicity, and the fact I got three trouble-free years out of her, driving her around CA and the Northwestern States. However, when I arrived in Florida, it became evident to me, that there were probably 75 days of the year that I wouldn't need A/C!!!! Since the car never had it . . . I wasn't going to even think about a retrofit, whereas, I would have spent the money to replace everything to get an existing system working. In fact, I did just that with my 300D which was the Pumpkin's replacement. I did not trust doing it myself. However, some 5 years later, and I have another set of leaks that need to be tested and refilled.
Personally, even if it's in the "Oven" states, I would hop on that car, even esepcially if the rest of the car has been mechanically well-maintained. I'd get the car on a rack, with or without an experienced mechanic, go through the undercarriage, and under the hood to see what needs (or will need) replacement, and start ordering parts for a couple of major "car clinic" days. I'd start with replacing belts and hoses, and work my way across the undercarriage (if needed), get an alignment, and with the alignment, a new set of good tires.
How much is your friend selling the car for???
And, if you're feeling a bit squeemish about the purchase, I'll gladly consider trading the "avocado" for it . . . .
Torie