According to
http://www.rockauto.com the clutch part number used on diesels is the same as that used on gas trucks of the same years and the 1980 4x4. The disc is 8 1/2 inches across. The problem is that the 1979 4x4 used the same clutch disc as the 2WD which is 7 7/8 inches across. You would need the whole works to make it go, clutch disc, pressure plate, and flywheel. I doubt the diesel flywheel is exactly the same as the gas version so even if you could get all the parts from the diesel you'd still need parts.
Redoing the clutch is such a major pain of a project, I'd really think twice about putting in used parts. The effort involved is up there at the point where you really don't want to be doing it again anytime soon.