beautiful furnace!!
I have not seen such a beautiful furnace since I worked in the home heating business in Quincy, IL!! What you have there is originally a coal fired furnace, door on the left is most likely the coal-bin. That brown box on the right is the blower compartment, 1936 they were starting to use blowers to move hot air, Lennox was the first to use a blower on their furnaces, the brand is cast on the firebox door. It could be Lennox, Round Oak, AFCO. I'm certain this is the original system, the way the ducts are run, its not gravity convection. This furnace would last centuries, the Brown box in the ash pan door is a gas conversion burner, looks the same as the one in my grandma's house on a coal furnace. This furnace would be something to keep indeed, it will last and last, if anything, add a newer system with AC as a separate system or a ductless system and leave this alone!! You wouldn't be able to add central AC to this old furnace, no way it would move enough air or be able to fit a tiny coil on top of that huge opening.
That furnace is going to scare the hell out of the typical HVAC Technician , beware of that LOL
More closer photos please!