Don't know if this helpful or not, but Benjamin Chaston of Mendham, nr Harleston sold his dairy herd April 1800 (Ref Ipswich Journal)
William Chaston of Middleton near Yoxford paying for gamekeepers certificate. Bury & Norwich Post 1812.
If you do have a Benjamin Chaston who died 1827 at Mendham, I can give quite a lot of info.
Have you also considered the possibility of the name also appearing as Chason or Chasen. Different rectors used their own spellings as thy heard the names being spoken. The reason I ask is because there are articles about people with those variations, much nearer to Snape.
