This.
Its a massive legal grey area. Both MA and the BATFE appear to exempt anything manufactured before 1898 as an item that is not legally classified as a firearm and any sale involving such a gun is not subject to any scrutiny and paperwork (4473s, background checks, and FA-10). So do what you need to do. If the seller will ship it to you directly, that is not technically illegal, if he wants to ship it through an ffl, he is just covering his ass in case any questions arise. However, seeing as it would not be classified as a firearm under state and federal regs, I don't know whether or not you would be required to fill out paperwork and show a MA gun license when you go to the gun shop to pick it up... Probably would depend on the ffl holder and his/her personal interpretation of the law, whether right or wrong or ignorant. Aren't gray areas fun?