I don't ever recall seeing an ash pan that small,I've emptied a lot of them in my lifetime.
The stains on the outside of the pan are reminiscent of the baked on carbon on cookie sheets and bread pans.The size is right for a large bread pan.The ends are folded in the same manner as my breads pans.The sides and ends are tapered for removing the loaf from the pan.It appears to be tin plated as are my older pans.I vote for it being a bread pan.
hasbeen