There's tons of this stuff still around, always has been. I never believed people even years ago who said all this stuff had been used up and scrapped. People always knew this stuff was special and tried to save it. Not always in big groups like your friends, sometimes just a piece or two in someone's garage or basement. It's of course sad when stuff that was once usable becomes too far gone due to poor storage though. Bits and pieces of rare cars end up getting scattered around and lost too. A little bit every year gets lost to some natural disaster also. Another sad fate is when the owner doesn't take advantage of getting this stuff new homes before they pass, and the family either junks it, or doesn't distribute it the way owner would have - maybe to car buddies who could do something with it. Something to think of though is our friends get older too, and aren't always able to deal with helping our families dispose of our stuff for us after we are gone.
One thing I would tell you, since you've gained some trust, is try to at least document the VIN's of the cars for the future, just in case something happens to them. I wish I had keep track of more of the stuff I found 30-40 years ago when I was scrounging. I'm sure you're a good friend Marc, just giving him someone to talk about this stuff with.
I love the GTE Cougar, it would be cool to see that running again. I had a chance for one about 35 years ago, but passed on it due to it having some damage and being non-running, just something I didn't have a way of dealing with at the time. You should help him get the wagon running too, then he could join our mid-sixties wagon owners club lol.