For the slotted drain plug on the transfer case I used the large flat screwdriver fitting from my impact driver and turned it with a torque wrench. That can work quite well but it is easy to chew out the inside of the plug if you're not careful.
For the raised square it should be 1/2" across so use an open ended spanner or you can put on a 1/2" drive socket upside down and then turn it with a large allen key from the other side. The bigger the allen key the more leverage you can get on it.