Glad I could help in some way. I believe Isaac was listed on the 1840 census in NY, Fulton Co Northampton image 7, age 30-40, wife ages 15-20. a boy and girl under 5.(As per 1850 Dane Co. WI.)
Perhaps the son of Jabez King III, b abt 1792 Woodstock Windsor VT, ( Elder)(Northampton -King's Cemetery),whose remains were removed to Dentons Corners, (Osborn Bridge) Cemetery in 1930. He was ordained a minister in 1810. " In the Christian Church for one year in 1821".History of Fulton Co., names him pastor of the Christian Church of Union Mills in March of 1818. Son of Jabez Jr. b 1 Jun 1769 Bridgewater,Plymouth MA, and Abigail Udall, b 11 Sept 1769 Hartford, Windsor VT. And grandson of Jabez Sr. b between 1718-29 Bridgewater MA, d 15 Feb 1813 Woodstock VT, and Mary Washburn, 25 may 1722 Bridgewater MA, who married 12 Apr 1753 Bridgewater.
Several Gifford families in the same area Fulton Co. Northampton, also.
If it doesn't work out, I'll always think it should have. Fits so nicely.Howard Boswell