just to catch me up, what is it you are doing/waiting on for the lower?
The lower has been engraved, and is assembled.
I'm currently waiting on my ATF paperwork to return, so that I can legally mate my lower to my 10.5" upper.
Is it the lower that has to be registered to have a SBR upper on it? Or is it a full auto thing?
Yes, the lower is the registered portion. When I receive my paperwork back I can slap on any length upper I want. For now I'll be adding my 10.5" Noveske MK18 upper to it. Later plans include an 8" .300BLK upper.
No full-auto.