Thanks all. I believe you are right Cliff about it being a diverter. That top on the cross cylinder has a flange on each side of it. So would make perfect sense and would further give me understanding of how it would work.
I doubt very seriously that it would have tubes in it. Boilers like we are used to have fire at one end and the hot gas is put through the tubes and released at the other end. So the tubes are necessary to get the fire in contact with all the water in the boiler. Faster more even heat.
But on this thing the way the fire is kinda built under the things i don’t think any smoke or fire is moving through them. I think it just sits on it like a kettle. And two small diameter boilers would heat up faster than one large one doing that.