Have a Miller furnace
model MGC-80-1
SN K397565
First time i have come across this model and serial number sequence
Installed in a mobile home?
I believe this is an aged unit before Miller was purchased by Nordyne.
I can’t tell you an exact age, but most likely mid to late '70’s or into early '80’s unit
Did it appear this age range and installed in an older mobile home?
some photos may help…