Dana 20

I just bought 1979 cj5 with a 304 and a 3 speed manual. I think the transfer case is a Dana 20 according to some of the threads I've been reading but am not sure. I'm having trouble determining the correct shift positions for the transfer case. According to other blogs I've read it goes 4h at the top, then 2h, n, and 4l at the bottom. However it feels like there are 5 shift positions when I go threw the gears with two low years at the bottom and two high gears at the top. Can anyone tell me if this is normal? Is there a way to know if 4 wheel is engaged besides jacking the jeep off the ground?