Martin - Dave is in Norfolk and is one of my second cousins.
The more I think about it, the more I am inclined to believe that Radcliff Bonnyman Killip is Boyer Killip. The name at Christening is not a normal one consisting of a grandparent's surname and an affectation and it is quite possible that he was called something else. Am I correct in assuming that you have not found Radcliff Bonnyman Killip in any records apart from the baptism record and that Boyer Killip appears in subsequent records, but there is no birth or baptism record? On the dates of birth - for this we only have Boyer's statement to the Illinois authorities for his Social Security application - it may be that he only had a vague idea of his birth date and made the best guess he could. I would welcome being proved wrong, but until the evidence emerges such as a death/burial for Radcliff or a birth/christening for Boyer I will consider the strong possibility that Radcliff and Boyer are the same person.