Do you mean post 427? I'd never noticed the difference until I saw the picture - it doesn't seem to register in real life, for some reason. The two vehicles have different origins: the red caboose is an LGB Toy Train model (repainted), while the green drover caboose was made from Bachmann Big Hauler combine parts, though the cupola which gives it the extra height is home-made. I built the main part of the body while living away from home, so didn't have any other rolling stock to compare it to, just assuming it would be the same scale as the rest of my stock. I'll go upstairs and compare them side by side now!
The home-made vehicle is built on a ply under-frames, so the "sit" may be slightly lower than when it was on its original frame. Looking closely, you can see the sides overlap the plywood, so this would make a difference in height of about 8-10mm to the top of the body side compared with the LGB caboose which sits on top of the under-frame.
Edit: Yes, I was right - the bodies are the same dimensions, just one sits lower than the other.