The little C223 2.2L naturally aspirated diesel engine looks tidy, but that might be because it hardly ever breaks a sweat while pumping out 58 hp. In 2WD form this made for over 30mpg in a pickup truck, but with the bigger tires and higher ride height of this 4-by, I'd say high 20's would be reasonable. My own former 1986 Hilux 4x4 with a carb'd 22R could do 25 mpg highway, if I tried really hard. But it didn't make that cool clack-rack-rack sound, and didn't have a baby blue air cleaner, so yeah.
This P'up ad raises more questions than it answers - who restores a 1983 Isuzu, and why? Under what circumstances does it get to share an airplane hangar with private jets and scissor lifts? Has any human ever actually sat in that seat, or grabbed that steering wheel? Regardless, this has to be the best example of the breed I've ever seen. The owner appears to be fastidious and I'd wager that it runs and drives like a proper little farm implement, albeit a slow one.