I have checked the Book of Dow to see if the information you gave is included, and was unable to find anything that matched what you have. It gives a Lydia Dow of Gilmanton m. Belmont Feb 5 1789, John Boynton. She is given in a list of unplaced Gilmanton records. No association with any other Dow is given for her.
There are many Isaacs and Simons listed but not any in the section dealing with the unplaced from Gilmanton. There was no Harriet Page listed as a spouse - and although a Lydia Foster appears in the index, I could not find her in the text.