there arent really any "body kits" you can upgrade to a regulator and on/off asa. i hate to sound like a CP fan boy but really it seems like everyone likes their products.
for a barrel you want spyder threaded barrels. from 12-16 inch and .685-.689 bore size.
cp barrel
http://www.ansgear.com/Custom_Produc...a1pcdblack.htm
cp regulator
http://www.ansgear.com/Custom_Produc...atordblack.htm
cp on/off you can go with 2 options
the rail and the dovetail asa
http://www.ansgear.com/Custom_Produc...raildblack.htm
+
http://www.ansgear.com/Custom_Produc...fasadblack.htm
or the direct mount
http://www.ansgear.com/Custom_Produc...fasadblack.htm