GAS SUPPLY The serial plate is located inside the lower front panel. It indicates the type of gas the unit is equipped to burn. All Southbend equipment is adjusted at the factory. Check type of gas on serial plate. These models are design-certified for operation on natural or propane gases. For natural gas, the regulator is set to deliver a 4.5" W.C. pressure to the manifold. For propane gas, it is set to deliver 11" W.C. If applicable, the vent line from the gas appliance pressure regulator shall be installed to the outdoors in accordance with local codes, or in the absence of local codes, with the National Fuel Gas Code, ANSI Z223.1, Natural Gas Installation Code, CAN/CGA-B149.1, or the Propane Installation Code CAN/CGA-B149.2, as applicable. This appliance should be connected ONLY to the type of gas for which it is equipped.
It could be converted but it would take resizing them orifices & pilot light, and getting an LP regulator. My opinion.