The Book of Dow has some information which coincides with yours - but some does not. Itgives WIlliam as b. ca 1750-1758. Acccording to the book he received a grant of 160 acresunder the act of 1783. He became a shipwright and settled in Milton where he d. 1838 or 1839 ; his wife Sarah Fowler b. Ulster County d. Poughkeepsie. After his death, his son wrote to Washington with hope of getting the land, but no transfer from William was ever made.Children listed were Job, Mariah, Jane, Caroline, Josiah, Hester, and Dorcas. The book has some additional information on Josiah and his children and grandchildren.
Book also says William had 2 brothers, John and Moses, who according to a grandson, came to NY City in 1768, their trade being forgemen. Their ancestor "could be" a William Dow who according to the 1790 census lived in Canaan NY with wife, dau. and adult son.
John built the first iron forge on Rockaway River.
The book lists this family in a separate section - not related to the other Dows in the book.
Neal Dow b. 1804 isa descendant of Henry Dow who came to MA from England in 1637.The book details him extensively.
Since William, Moses and John's parents are not identified, it isn't possible to link them to the Henry Dow descendants. It also was assumed that their father may have been an immigrant from one of the industrial counties of England.
If interested in more details from the book, please email me.