And possibly a new cross member depending on which one your truck came with. Dodge used two different styles on the 99's, some work with the 6 speed and some don't.

 

Your t-case will bolt up being as you already have a stick truck. You dont need to change the crossmember either although good luck getting it in and out. When I converted mine from auto to 6 speed I used the stock crossmemeber and a 3rd. gen. trans mount. You will have to modify your driveshafts. Converting mine from auto to stick I got a new front shaft w/ my NV5600 and shortened my rear shaft 5". Hopefully this answered some of your questions.

 

Updates??