I can't get over how large this model will be once completed. Photos just cannot do its size justice, but the picture above shows the main frame next to a foot-long ruler. The thing to keep in mind is that this is just the engine. There is an entire tender that will be following behind.
One of the things I recommend when constructing the engine undercarriage is to leave the cross-member pieces unglued until you can get it squared and clamped. The model had a nasty warp in the middle that I was very concerned about. Had I not clamped the undercarriage between two straight edges and then glued everything in place, I would likely have had difficulty getting the wheels to line up on the tracks later. In general, the fit isn't quite like newer kits.
Yes, I realize I am completely ignoring ejector pin marks. I hate filling them and don't want to mess with it. I will take care of any obvious ones but these will be hidden enough to not bother.