I've also been trying to solve this problem for a while as I am a descendant of Thomas Elton. Yesterday I finally cracked it you will be pleased to hear!
I too believed this Thomas Elton and Sarah Grace married in Longstock in 1779 were the parents of Henry born in 1780 in Newton Toney but why did they move the short distance over the Hampshire-Wiltshire border was a mystery. Sarah Elton's burial entry in the Newton Toney register dated 16 February 1834 listed her age as 79 which suggests she was born in 1754 or 1755. This initially pointed at a Sarah Grace who was born in Bristol in 1755, however, I have long wondered if in fact the correct Sarah Grace was one christened in Over Wallop 16 March 1760, which is no more than 6 miles from Longstock? Could it have been that she was 74 when she died and the Newton Tony church record was incorrect?
Quite by chance sitting with my parents in their front room yesterday, I discovered a transcript had been made of the marriages at Newton Toney from 1591-1812 and was available for free on the UK Genealogy Archives website
www.ukga.org On first review I remarked to my parents crikey there are two Grace girls getting married in Newton Tony in the 17th century. Further review brought about a major discovery. Listed on 15 July 1759 was the marriage of Edward Grace (of Over Wallop) to Mary Quaite (both widows). The light bulb moment was confirmed when reviewing Sarah Grace’s christening record of 1760, her parents are listed as Edward & Mary. Mary Quaite maiden name was Mary Tinham. She was christened in Allington on 4 Jun 1727 & had married Edward Quaite on 9 Jun 1752 at St Edmunds Salisbury although her residence was Allington. Edward Grace was christened in Newton Toney on 29 Jan 1727. He first married Betty Hayter in 1750 in Winterbourne Earls. They also had a son John in 1753 baptised in Over Wallop.
Finally I had established the link between Newton Toney & Longstock and a credible explanation as to why Thomas and Sarah moved - family ties.
