The types of kits that use the late model GM parts have their place for budget builds. Iron hubs/calipers with bulky slip-on rotors, however, aren't exactly light setups. Kore3 is another option and their hubs also allow for heavy duty 1/2" wheel studs to be used.
http://kore3.com/
If it is at all possible, I would save up a little cash and chase down a Pro-Touring F-Body kit which uses Wilwood components. Aluminum hubs/calipers and lightweight bolt-on rotors make for a nice lightweight "big brake" package. I'm actually using their A.X. Special kit on my 2nd gen. These kits use heavy duty 1/2" wheel studs and can also be upgraded to the 13" brake setup just by changing the bracket and rotor.
http://pro-touringf-body.com/brakes.html
You can also swap out your stock calipers for aluminum twin piston D-52 calipers from Wilwood. This would allow for stock size 15" wheels to be used. PTFB and many other vendors can supply this.
Hopefully my input helps puts a broader picture in place. The big brake kits will require big wheels.