W56's came in both forward and top shifting configurations.

If you have a G-series tranny to begin with, the transfer case won't work without some modification if you attach it to a W56, even if it's the same shifting style. The forks are slightly different lengths.

BTW, something I recently learned is G-series transmissions have 8 bolts around the input shaft cover. W56's have 7.

Not knowing what you're starting with, the best bet is to grab the tranny/transfer pair from the 91 instead of assuming your existing transfer case will work with the 91's transmission.

With a compatible tranny/transfer combo, top and forward shifting setups will both work. If switching styles (at least when going from forward to top) you'll need to cut out the floor to make room for the new shifter locations.