Alright ya'll...here's the update. I spoke to folks at the State Firearm Records Bureau, several other FFLs, and the local PD. All have verified that a valid DL is all I need for the FBI background check (form 4473). This guy is telling me :
"You will need to produce two forms of picture ID that match your current address. A list of acceptable secondary documentation is available on the ATF form 4473 Section C question 26.A and 26.B."
Now, I know he is incorrect in his interpretation of form 4473 Section C question 26.A and 26.B. It states clearly that a DL is all I need. But I also offered tax documents, car registration, and even a copy of my LTC validation certificate straight from the MERCS portal. All of those documents are valid forms of supplemental identification per the ATF. He still refused. In fact, he rudely told me on the phone that he his just going to ship it back to the original sender and then hung up.
WHAT A ROYAL PAIN IN THE ASS!!!!
And for those that want to know who he is... His name is Peter DiAngelis and his store is North Falmouth Hardware and Marine. Nothing but rude from the moment I walked through the front door.
One last thing... I will be making sure a gunsmith looks over the pistol thoroughly to make sure he didn't mess with it. If he did, I WILL sue him into oblivion.