Yes, there might be a problem, there was a Halfdan the son of Sigurd and Asta and an elder brother of Harald Hardraada (or something like that), the King of Norway who died at Stamford Bridge in 1066, but I'm not sure if the death date of 1047 is correct, this might be someone else?
Nor can I find anything in Heimskringla that indicates that Halfdan was called 'the Old'. Given the common names perhaps their should be a bit more investigation before the merge takes place?