Hard to see how that is a "rust bucket" in that pic? What rust?! Or am I just looking at it with my Michigan eyes?
Her cousin had it for awhile. He had it parked on the side of the house so all the rain run off from the roof landed on the car, leaked in the old rotten vinyl top. It rusted all around the back window allowing holes to form and leak into the trunk floor. Its rusted through too. Her cousin also sold the gas tank out of it.
All the floor type replacement panels should be the same as an Impala, so very available and plentiful as well as around the back window should be very close to the same so those pieces should be obtainable. The roof should be the same as the Impala as well and might be some patch panels for that too? The stuff that would be hard fix or to get your hands on to replace is the solid looking outer body panels that the car already has. Even if the frame is rotted, it would still be worth getting a nice used one for it to put that body on with new floor pans where needed. But I'm not as afraid of that kind of work as others are. There are Impala frames('65 to '70) that go up for sale that are still priced reasonable if it needs one of those. If it doesn't need a frame then it would be a no brainer to save that car from the shredder!(or sell it to someone that will save it)