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
// Nexus 5 (D821) // Paranoid // UBER //