I cannot find this particular furnace model, the only information that is showing up in search is for Suburban DCF-30G residential furnace that was manufactured first time in 1987. There are many Suburban furnaces available for RV’s but those would need to be converted from LP to natural gas.
Most if not all of the furnace manufacturers make gas furnaces which can be installed horizontally above the ceiling. Installation would depend on the amount of space available above your ceiling to accommodate this new appliance, configuration of air ducts, the vent pipe, and overall location of the furnace area.
If you can fit one in the same space that your old Suburban furnace currently occupies, your choice would be between a high efficiency unit which utilizes PVC pipes for venting and combustion air supply. You wouldn’t need a chimney, just a way of getting two PVC pipes to the exterior (through the side wall or roof).
Second option, a horizontal, regular efficiency furnace using existing chimney and combustion air from the interior of your house.
You would probably need to get a heating contractor to check your current installation and look for a unit that would fit into that space.
Let me know if you have any other questions.