Age help Lennox

The only information on the unit was Lennox GH6-120-M. Thanks for any help. I am guessing 60’s by condition of unit, but would like to know for sure.

See this

Thanks Mike!

Hi, hope i’m in the right area. I live in a home built in 1959. The original furnace is still working, a Lennox GH6-140M. I want to replace the old thermostat since it is not accurate. Could you please point me in the direction to one that is compatible?
Thank you!

Preston’s guide - 1965-1969