A box is often not needed for a stockish motor (even NA up to around 400 HP), so we might assume you have some goodies that you're not telling us about (which affects recommendations).
I was thinking you may be able to open the gap a bit if you wanted (to 0.060" territory). I see plug gaps like timing - you gotta keep upping it until it starts to get a high RPM, high load miss, and then back it down.
Even with a stock gap, the spark should allow a better burn.