Thank you for your advice.
To go into more detail, we have a (I believe) 1/4" or slightly thicker steel frame, insulated both under and over the firebrick with refractory cement.
As an Update:
We switched out all the pipes to slightly smaller diameters and redesigned the nozzles so that they could be adjusted. Seems to be working now using only two burners.
So now we are going to see about setting up for a second tank to provide adequate pressure.
To answer your question, yes we are working on swords, longer axe heads, and other similar weapons. The nozzles are around 6 inches apart. If you think this will be an issue for even heating, what is your suggestion?
Again, we will have doors on both sides that can be closed and opened.