Yes, inline engines are great engines. Not just the 4.0L. Dodge had an old slant 6 that was bullet proof and Ford made the old 4.9L 300C.I. inline 6 that was a 400K mile engine too. Of course Honda and Toyota 4 cylinders are inline engines and are known for longevity also. It is the design of being inline that is part of the secret. The engine does not work against itself as in a v engine. Of course the old inline 6 engines are not as efficient as engines are today with MPG and horse power too, but they are long lived engines when taken care of and serviced well.
My pappy was a pistol, I'm a son of a gun.