I'm going through the process right now here in MA.
There are no special licenses needed for an SBR here in MA, only MG's. If your friend can legally possess an AR15, he can legally possess an SBR'd AR15.
If the lower being used as the host for an SBR is a post-ban, then yes, it must comply with the MA AWB. I've heard both ways argued, so I contacted Chief Ron Glidden of Lee, MA (THE firearms law authority in state) and he said that the AWB will still apply. That's why I got another pre-ban lower to use for the host.
Now, state registration. If your friend already has his lower registered on an FA-10 when he purchased it, then he's all set. If not, when he gets his Form 1 back and assembles the SBR, just fill out the FA-10 as he would for any other completed AR15.