Well there are a few Foster Dunwoodys around so you'd really need a little bit of informaton to decide which one it is, possibly there might be a townland or something on one of your previous marriages that could point to the correct family.
Other than that you could look for Samuel's parents marriage cert, as Civil Reg for them would have started by then, you should get townland. Then look for Dunwoody in that townland to get the correct one.