Watched some Hoovies Garage on 911's, that's some potentially deep water you're wading in
On the other hand it seems the value of these things has gone nuts, so maybe you can't lose
I don't think Hoovie has done any air cooled 911 stuff, though has he? I believe most of the problems he had were with the early liquid cooled motors.
I think all the air cooled cars are pretty much known entities, as to what to expect, and how much money will need to be put into them. Like, at some point, the engine needs to come out, be split apart for some major service/rebuild. Big indicator here is if it starts to burn oil (I think? I'm not a porsche expert - just what I've absorbed on the internet here and there).