You can do any of them, but what you end up with depends on which dana 20 you have, because they shift differently.
My early bronco 20, one stick controls rear axle, one front, so now that I removed the lockout pins I can get rwd, fwd, or 4wd in high or low range. However, without the lockout pins it IS possible to put one in high and one in low.
If I am not mistaken, the jeep 20 one stick controls 2wd/4wd, the other hi or low range, so I'm not sure that twin sticking would get the results you want.
On mine, in order to get fwd you have to remove the lockout pins. They are located BETWEEN the shift rails. This means that you have to get the shift rails out in order to remove the pins, which means basically disassembling the entire transfer case to get the shift rails out.
Hope this helps.
Chad