Check out the Scout section on Off-Road.Com too.
I have a twin stick on my Dana 20, using Dana 18 sticks. The detent isn't strong enough on the rear output shifter and it tends to pop out of gear. I've heard of this problem with Dana 300 twin sticks as well (Tera 4:1 kits even address it by putting a deeper detent pocket in the replacement shift rail). You may want to drop some small washers under the spring for the rear output detent to make it stronger if you have your T-case apart already. I wouldn't bother with it unless the T-case was disassembled though -- of course I am using a bungee to hold the rear output in low range on the trail now