That's not a Yukon...it's a Mendota.
The guys that made them tried to copy our furnace only with the patents that were in place they could only go so far...NO REBURN...and no where near the heat exchange surface area. To buy this furnace without any parts available is taking a huge risk....not to mention it's not listed which does not meet code. No way is it insurable.
That unit is a good 25 years old. With it's age being so old I'd say that there's not that much left in her.
If it had been a Yukon there is an oil to gas conversion available.