Look at some videos of Baker steam traction engines and you will see that they have a round bottom on the firebox. The water legs totally surround the firebox, going down and around under the grates. Repairs nowadays switch them over to an open bottom, so we can assume the plan is to make the new boilers last more than 100 years! No more mud to work on the steel down at the bottom! Note the rivet heater. It was patented in 1913. It's a first time for me to see one of these!