This is a good thread.
I found a 65 coupe last week while I was driving around during the town wide tag sale, and a road I never go down. The car was in really good shape and in a driveway with a for sale sign but I had no interest in it. Surprised to see it though, never seen it around and was likely put out only for that weekend to see if they would get any bites.
I know of 2 Mustang fastbacks sitting in a yard for the past 20 years, one has been rear ended so hard the tail panel is where the back seat should be. Don't know the condition of the other. I heard about them from a guy in work that his neighbor has them. I've never seen them or have any other info but he's trying to find out more when he gets the chance. Trying to find out what years and possibly pics. Might be some decent parts left. They are deep back on the property, not visible from the road, and unfortunately likely won't leave the property whole as there's no vehicle access to them anymore due to the land being regraded years ago. A helicopter may be the only way to remove them intact!