You are absolutely correct about that. That had actually slipped my mind yesterday. I have seen several run successfully with that boiler style, and Charlie's has that cast bronze boiler firebox and rear section. In my generalizations, I kind-of lump them in with the copper boilers because the front section still is copper and has to be silver soldered onto the rear sections. That whole 'boiler casting' was Little Engines' attempt to make a boiler easier to build and a lot less expensive. I have heard that some of them worked fine, and some had a lot of porosity and voids that made them nothing more than fancy door stops. I've heard of a few of them being brazed up and used also. You can almost break boilers down into two types: Welded boilers and soldered boilers. I know that's not exactly true 100% of the time, but it works for describing boilers and their build methods to most people.I'd say most LE Americans and Huntingtons used LE's bronze firebox casting.
Main Point: If you have a copper boiler, then take care of it! I think Charlie looked into what a new copper boiler would have cost for his L.E. American, had that one not been usable, and it was something like $8,000 a few years ago. That's why a lot of people go with a steel boiler if they can, especially in the larger sizes.