It's a boiler, not a furnace and it's leaning to the right. Pre 1984, Peerless did not use a date code. From 1984 to 1999, the serial number ends with for digits. 123456-1092 would be Oct. 1992. Since 2000, the serial number ends with 6 digits. The first four of the ending 6 digits is the year. 123456-200206 would be June 2002. The auto gas valve has an ink stamp with the date. Compare that to the numbers on the PRV valve handle or tag. One of them would likely be original.