Not sure the best place to ask this but does anyone know what year the first Ford factory dually 4x4 was made?

Not cab and chassis but a regular pickup with a box dually 4x4?
I say 1986 but the guy Im arguing with says later.

 

I believe the correct answer to this is 1999 for a direct from Ford assembly line 4x4 dually. Far as I know all the prior ones were conversions done by companies like Centurion.

But I've been wrong before