Bryan - Are you still trying to get in touch with the State Police with clarification?
You might try the Massachusetts Firearms Records Bureau
http://www.mass.gov/eopss/contact-us.html#a3
http://www.mass.gov/eopss/firearms-reg-and-laws/frb/
If they're no help or cannot refer you to someone else, I can ask around on Northeastshooters (NES) for a good lead as to where to get clarification on the laws. It may be the AG office.. Who is about as helpful as the bully at the school playground.
I digress..
In other news, irrelevant of the item in question, whether it be a stripped AR lower, a MA Compliant AR or a 1911 - the onus is on the MA State FFL for abiding by the laws and doing (or not doing the transfer), not the vendor. After all, this crazy state loves to change things - so I can't blame you for covering your bases.