You would likely only need 1/2" to 5/8" of transfer case skidplate drop which can be achieved with washers between the frame and skidplate placed around each bolt. Due to a depression in the skidplate you would however require probably 3/4" or 13/16" stack of washers to actually drop the t-case 1/2". A 1" MML would do it too though it's more difficult to install and you really need a helper to do that.
If you install the t-case drop kit or washers, remember to support the skidplate in the center with a jack and don't remove all six bolts at once. That makes it too easy for the skidplate to shift out of position and make it harder to get the bolts back in. Instead, leave the bolts threaded in loosely on one side and remove the other side's bolts. Insert the spacers or washers and loosely thread the bolts in then remove the other side's bolts.