That furnace was subject to Suburban's recall due to the rubber crossover tube which supplies the combustion air to the burner. Suburban no longer supplies the recall part or any support for the furnace, unfortunately. So a heads up, you really do need to pull the furnace and check to see if the rubber tube in the back has a red stripe on it. If it does, it has had the recall modification made. If not you have a potentially dangerous unit. You cannot see it without furnace removal.
The same furnace in my '71 Caravel
kept giving me headaches and the windows kept fogging up badly in cool to cold weather. It turned out to have a rusted out combustion chamber (but it did have the recall modifications). Please be careful. Of course I replaced that furnace.
The NT 16 that came in my '74 Argosy 20 was in good condition, and had the recall modifications, but I replaced it as I wanted electronic ignition rather than a pilot light.