While the 100-acre Shackford holdings along Water Street underwent subdivision and real estate development, the 100 acres at Shackford Head remained intact. So far, I’ve been unable to locate the original title that would have been bestowed by the Commonwealth of Massachusetts to Captain John Shackford senior, but the documents for the adjacent Coney or Cony Farm repeatedly refer to the land held by John Shackford, during his life, or later, “land formerly of John Shackford.”
In 1837, when Joseph Coney leased his 40-acre farm to his son, Samuel May Coney (1812-1895), the rent was recorded as one cent a year.
Samuel soon came into full possession. By the time of his death, he had added the Shackford property, too, as was noted in the sale from the estate (attorney John H. McFaul) to Charles O. Furbush in 1896. That transaction included an 1895 Plan of Shackford Head by surveyor H.R. Taylor.
All of this would become part of the controversial attempt of Pittston Company’s attempt to build a massive oil terminal and refinery on the site in the 1970s.
I can see why Shackford heirs living in Eastport would have held onto the rugged land. A house could go through 40 cords of firewood in a year, and with seven homes or more at times, having a large wooded reserve would have been useful. Depending on the proximity of a sawmill, the wooded land could have also supplied the Shackford shipyard or even the wood in our house.
Jnana's Red Barn 
One possibility for finding deeds: https://www.familysearch.org/en/labs/. Pretty amazing tool that searches through handwritten words and finds many of the documents stored at familysearch.org and transcribes them for you – the transcription isn’t perfect but it’s a good start. The deed I just found referenced land purchased in 1834 from John Shackford from whom he purchased land in 1834. (deed recorded in 1841). That deed mentions that this is part of land of John Shackford’s land being part of lot number 15 on Benj R Jones’ Plan of a part of John Shackford’s land dated Aug 7, 1810. Does take a bit to update these transcriptions but I do attach them to the individuals listed in FamilySearch so they can easily be found later.
There’s apparently a box of very early records at the Machias County courthouse that have not been entered into the database. Add to that some of the delays in recording the deals, as you’ve encountered, and you know how it gets tricky.