First, welcome to the board, post some pix of your rig when ya get a chance...No, you don't have to change the steering linkage. But depending who you get the lift from, and what type of lift you get, most come with almost everything you need. Yes you will have to extend or buy a longer rear driveshaft and it is recommended that you do the same with the front, but you don't have to because there is actually enough slip for a 3.5" lift in the front shaft. You will need new extended brake lines, drop pitman arm or track bar riser. Some companies sell those with the kits but most don't unless you buy an extreme kit. I would recommend getting the Cage 3.5 kit. (
http://www.cageoffroad.com ) Cage does recommend converting to the T linkage though. It isn't a tough conversion if you have any mechanical skills, but it can be time consuming if you are a novice. Most lifts are pretty straight forward and if you do order one from any of the vendors (BC Broncos, Wild Horses, James Duff, Tom's Bronco, Cage) I would call them and ask them questions. They are all good on customer service and will help you out.