Even with an SL, the front shocks don't need to be longer, as even if its the SLR SL, with a couple more front droop inches, the stock shocks are STILL long enough to reach.
The ONLY advantage to getting the Bils up front too, is that the truck will ride/handle better...not because the front stock shocks are too short.
The Bils you order for the 3" SL use the same length shocks up fron as stock...they're just valved differently.