Have you looked underneath? The transfer case came with a big red circular tag that tells you which model it is.
I have the NP208 in my J20 that is extremely simple to use, slick in action and tough, but it is not a permanent 4WD, just selectable. Depending on transmission etc you may be able to fit one of these or the later NP cases, NP228 and NP229. The NP229 was in the Grand Waggie in those years, so you may find you actually have this and not the NP219.