I don't know if you already know this website but if you click the link, then scroll down to 'Shepherd Family Ancestors', then scroll to 'Surname List' then down to 'Wood' you'll see Mary Ann, the children and her husband listed here. I think whoever runs the site has researched on the assumption that 'Peveral' is 'Powell', the same as you mentioned that William Powell should be William Peveral, in the 1851 Census

http://fh.sheppardfamily.us/
Hope this may be of some help