Ron,
What part of caboose #4 do you think was used to create this coach? Since the caboose was shorter the truss rods would have to have been reconstructed. Perhaps the queen posts were there. The end railings and grab iron are completely different. I think the caboose was sitting on shorter freight type trucks, but I haven't seen a good photo to confirm this. There aren't any chimney ventilators on the caboose and the caboose had long benches for seating on both sides of the car. Due to the shorter car body, different size and shape of the windows, etc. it doesn't seem like any of the car frame would be reused. Maybe the couplers were reused, but why not the end railing and grab irons. I don't see that much was reused from a deteriorated caboose #4. Parts could have been collected over the years from various sources to detail the rebuilt car and perhaps they were nicer than those on the caboose.
Dave