Hicks,
If you're already reloading, that's a good start. Hate to see guys trying to load for gas guns without having a solid background in reloading for bolt guns and the like, since this is an advanced form of handloading.
No you (probably) won't need SB dies, but they won't hurt anything, either. Most ARs will get along fine with standard F/L dies, especially something like the Reddings, which tend toward minimum dimensions anyway. Get a gage if you don't already have one, and use it when setting up your sizing die. Make sure you're bumping the shoulder enough to provide at least .003" clearance. Again, these aren't bolt guns, and they need to be treated differently. I might suggest some of Glen Zediker's books or website, since he deals a great deal with reloading for gas guns, specifically. There's a chapter in the Sierra manual on this, as well as some excellent material in some of the specialty books put out by Sinclair and Precision Shooting magazine (all of which should be available through Sinclair).
Hope this helps, but don't hesitate to let us know if you have any questions.