First of all it’s a lot of asbestos on those pipes . So you kinda need to figure out how to remove Al that asbestos wrapping around duct pipes. Second that furnace probably 50-60% efficiency. That furnace was supposed to be replaced 20 years ago . I would bet my money that it has cracked rusted out heat exchanger.
Last it should go some museum that shows furnace history.
Change it and change it now.Not safe and wasting your money.
You can look so some guy on Facebook or some other sites on media and get new scratch and dent unit. High efficiency can be bought for $1000 and install for $1000 . So 2k and you got nice new furnace