As I was studying my rear diff yesterday I noticed how smoothly, seamless, the pumpkin transitioned into the tubes. I was studying this because I was contemplating welding on it and have read many posts on here about welding on cast iron. I have read that if you need to weld on the tubes, go ahead, but if you need to weld on the pumpkin, you better preheat. There is no obvious transition from cast to mild. Is the top of the pumpkin really cast iron? Anyone really know?