ARB sells a t-case lowering kit for about $40 I think.
This includes 1/2" spacers and 6 new longer bolts.
Or just make your own.
Pull one of the bolts out (the tcase should be fine with 5 bolts for on road driving)
Take the bolt into a bolt shop
and ask for the same thread but just 1/2" longer.
Then just make a spacer using a stack of washers or whatever suits
simple as that
cheers
z