I know the 492 after it was hit by a falling rock ended up getting 490's smokebox door, and had about a foot section of the top half of the front replaced too. They used welders. Of course they had to either cut the piece they needed off of the 490, (which actually I think they did) or they formed a new one.
Look at John West's websites. He has a photo of the 490 on a flat car in Alamosa in the mid to late 60's. You will be able to tell by this which parts of it's smokebox they used for 492.
Earl Knoob showed me the rock that hit the 492. It's a big one! That probably would have made a nice boom when it hit because of the sheer size of the rock, and the pressure in the smokebox. Did anyone get any pic's of 492 in this state?
Kevin Bush