I get that cash isn't falling from the sky, but are you sure a furnace old enough for it's own AARP card is even worth fixing? Even if you found something to make it work, the money might be better applied toward a new, more appropriately sized furnace. A typical lifecycle for residential hot air furnaces is more like 25 years, after which anything other than the most minor maintenance & repairs are usually a poor investment. This thing is twice that age.
Furnaces are typically more than 3x larger than needed, and while they heat the place they're less comfortable and noisier than something with 1.4x (or less) output capacity than the heating load at the 99% outside design temperature. At ASHRAE's recommended 1.4x oversize factor on the 99% load you still have sufficient capacity to be able to use overnight setback strategies without glacially slow recovery times, and enough to cover the load during Polar Vortex cold snaps.
If replacement is the path you end up on,
run these numbers first to right-size it. Most houses with 125-200,000BTU/hr furnaces can be heated with a 40,000-60,000 BTU/hr condensing furnace, but not all. Some are even better off with a 30K furnace.
