I have knowledge of 1 Dudney in Devon as at 1881 census but not yours, although prior to that date there were lots of Dudney's in Devon. Dewdney Dudeney are all derivites of Dudney the 1881 census shows Arnold A Dewdney born 1869 Brixham Devon but nil Issac. shows an Issac Dewdney grandson of John & Jane Hine. The census shows 2 Arthur Dudney's born 1867 and 1869 in Sussex no Duncan.
It showed 130 Dewdney's 1 Dudney and 1 Dudeney in the South West of England. Hope this is of help.
I would be interested to here of any more details if you find any.