Green-dot
I've seen 2.50 USD/USG figure more than 10 years ago and that was 62/63F vs 72/73F, have you seen the same material by any chance?
DC8 is maintenance extensive airplane comparing to next generation (like 757) and if you want to maintain it properly you would not be competitive on the market which is almost solely driven by $/kg/nm.
There is always a good reason why this or that aircraft model was phased out from so called "developed countries" fleets. Africa is a different story.