make sure it has been well maintained, looks good, doesn't leak fluids, has good tires, good fluids, isn't muddy or greasy as well, etc.

a common issue is with the mikuni carb, they are just crappy carbs
another is with the jet valve heads cracking. its a week spot because the head is thin there
another is the timing chains. replace them often. preventative maintanence is always good

also do a compression test, fuel pressure test, check the voltage of everything, make sure all the gauges work, all the belts are good, and make sure all gears shift smoothly and that 4x4 operates properly in 2H 4H and 4L. make sure the brakes are good and that the parking brake functions properly and is in good working order. check for cracker/broken suspension parts, and maijor rust. and don't forget to check the fuel filter while you are under there.

expect good gas mileage and plenty o power outta that diesel!