Valve upgrade for TSP LS6 heads
I believe that 2.02/1.57 is pretty much the optimal size for stock cubes. You also don't need new valve seats for the 2.02/1.57 size either. Anything bigger I think you'll need new seats put in.
For the best possible flow with stock seats this combo is very hard to beat. We're putting together a run of those stage 2.5 LS6 heads right now. They are on special for 1499 with springs & 1250 without!! 

