Explorers only came with one transmission for the 4.0 in that year. Check a web site for a tranny shop for the model you want to put in and it will tell you if it is possible without major alterations.
If you are looking for hard core offroad ability you might be able to add a dual stick transfer case or a set of lower ratio gears into the existing transfer case. I know that you can do this with some 4x4's, not sure about yours.
Search Ford Explorer Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Ford Explorer Experts