I am trying to find the grave stone for Nehemiah Samson too. I just found a copy of his marriage certificate to Bathsheba Baker at the Stoughton, MA town hall.
I also found and photographed the gravestones of his Grandfather (Jonathon Samson Sr.) and grandmother (Joanna Samson), plus the gravestone of his Great Grandfather (Isaac Samson). I'll travel up to Rochester, NH next spring to look for Nehemiahs stone. I've also located the land in Duxbury (this is where he lived),where Nehemiah's Great Great Grandfather (Abraham Samson) is buried in Duxbury. I found many Samson stones in Duxbury, so I'll be scratching the land there to see if his stone fell over and is reating just beneath the surface.
If you could email me your best guess of the exact location of Nehemiah's stone I'll go there that look for his fallen grave stone. My email is firstname.lastname@example.org