I've had this old furnace (Lyman MM 20lb) for some time that picked it up cheap at a gun show. It was nasty dirty and rusty but disassembly and a steel wool cleaning plus repaint made it like new. I've been trying to date it's year(s) of manufacture. None of my old loading manuals shows this particular model. All I find is the 10lb Lyman 61 furnace with the thermostat on the front. Any info would be appreciated.