A buddy has a 70 GTO Judge when he was thinking of selling it 10+ years ago I did a search on ebay of like vehicles and the average selling price was $28,000. So a current market value of $40,000+ isn't out of the realm.
I'd suggest starting with the National GTO club
GTO Association of America and see what they say. A unmolested car with no accidents will peak their interests and a private selling to a interested party is the fastest way to move it with less hassle to you and your friends widow. Send them the pictures you posted here and who knows they might write a article about the car for there house magazine.