I have a similar goal and assuming the transmission and transfer case are already taken care of and everything else is in good working order you will have to go dana60 to spin 40"s. your 4.0l can easily spin them and if built properly it will be able to put out the torque you need to even spin them fast enough to clean them out. I am going with a leaf sas because it is easier and cheaper. Either way it will cost way more than 2k to get it done for you, and to do it yourself should cost around 3k. That's my estimate based on my experience,I don't know all your details.