The baseband is NA2 and the build number is NA6 they're one and the same afaik.
As for installing a custom ROM well you can install NA6 based ROMs only like flexkat, sweetrom kingdroid and crashrom. But not CM or older builds of said ROMs.
Sent from my SM-N9005 using XDA Premium 4 mobile app
// LG G3 (D855) // Stock // Stock //
S3(White) > M7(Red) > Note 3(Black) > Nexus 5(Black) > M8(Gunmetal) > LG G3 (Titan Grey)