It is frustrating searching family prior to easily available public records, here are a few things I will usually try. Find a McGeehan sibling of Daniel by searching obituaries in his location (emigrants at that time period usually already had family here or some that joined them later) and the Baptismal sponsors of his children. Hopefully a younger sibling of Daniel's ( they had large families) will appear that was born after Civil Records commensed (1864). It looks like Daniel was born right around the time of the Griffith's Valuation (1855-59 in area you are searching) and that record is often used as a Census substitute, most likely his father would appear in that record. For example if that is the correct passenger list you cited it looks like he was traveling with two older brothers, John 23 & William 25 (they likely all resided close to each other here) and since William appears to be the oldest you can take a chance he is named after his father (however more commonly after their gfather). If that was the case the GV records lists 100 McGeehan households in Donegal but only one to a William (Lettermacward, townland Commeen), I did not see any "William" McGeehans in the 1833 Tithe record but did not check all spelling variations. Certainly no "smoking gun" but perhaps you can keep that townland in mind in case some future discovery points that direction as well.