just do the 4.7 gears in your single t-case.  Just did that to my truck and love it.  pretty easy install as well.

reasons for me doing this is:  -planning on lifting my truck in the spring, so i didn't want to have to modify DS twice if i went with duals
                                        - when i do go to duals when i lift it i will be modifying DS once, and when i do duals i will have an ultimate crawl set up 223:1 crawl ratio

that is my reasoning for only doing 4.7s in single case right now.  right now i have  a crawl ratio of 72:1, if you were to just do single 4.7s you would have a crawl ratio of 89:1.  reason being you have 4.88 gears in your diff. and i have 3.90 gears in mine