Duals will get you your stock low range of 2.28 to 1 along with 5.2 to 1 (2.28*2.28). Going straight to a 4.7 box is nice but you will lose your stock low range. On most trails, I usually am running in my 4.7 box, front case in high. If it's an easy trail, I've got the front box in low and the rear box in 4H (aka stock low range). You could get away with a 4.7 box only, but you'll be in 4th & 5th gear between obstacles on most trails.
Did you end up with that 4Runner in your first post? What size alcan springs are on it? What size tire are you planning on running? If you plan on running trails no tougher than Holy Cross, I'd suggest 35's and 5.29's to make it easier to get around town and up the mtns. 35's will take you anywhere you want to go.
