Zach, usually the drain plugs are 24mm for Land Cruisers. At least on the diffs and tranny they are. I think the t-case is 17mm. Get you a 1/2" drive 6-point socket or even an impact socket (thicker wall, less deflection) to help. But before taking off the drain plug take off the fill plug and make sure it doesn't strip out on you (you don't want to drain the oil only to realize you can't refill it). And consider investing in new drain and fill plugs, possibly allen heads. They can be had at the Toyota dealer. I have some sockets you can borrow if you need but I don't get up that way often.
Sometimes heat will help loosen things up. Try to get the area surrounding the drain plug hotter than the plug.