Per that thread, 2.5 qts for dual t-cases. I have almost 3 in mine so far and going to check it again. I'm expecting it to take closer to 3.5 qts. Takes a good bit of time for the gear oil to work its way into the crawler box when filling it up though the rear fill plug.
Good suggestion I heard is to fill up the crawl box though that shifter, and wait for it to drain out the rear t-case fill plug. Takes time to get though that bearing so wait till it stops draining.