[LS short box]

I would give Tobin at Kore3.com a call. He sells brake kits from mild to wild. He can also spec out the MC that you will need.
If it's in the budget I would go 14" in front with your 20" wheels. The 14" rotors fill up the wheel quite nicely.
On my 68 C10 I'm running C5/C6 14" front brakes and 1997 Camaro 12" brakes in the back.