Thanks for that Spats. Unfortunately, it still doesn't clearly answer my question. At least I'm not confident enough in my understanding of it's verbiage to consider it answered.
I'm a bit confused by their definition of "firearm", and whether their ruling applies to manufactured kits only, or if it covers kits by manufacturers and kits thrown together by Billy Bob Backyard Armorer.
They talk about what is and is not a firearm when it seems to me the proper verbiage would be what does or does not constitute an NFA firearm.
Still confused.... :/