I left Greenock Scotland in 1962 now reside in Kent England. My son lives in Syracue Utah, so I have been to Idaho a couple of times.
I tried all the names you gave with Duncan but got nil returns, although I believe I found Angus and his wife. I have always taken Scotland's People as the authoratitive source of all official scottish records, it will be interested in seeing their response to my query.
If you have something on Duncan around 1861 that is good news. Prior to 1855 death records are few and far between. In the 1851 info you sent Duncan is shown as 60, so at 1861 he would be 70ish, at that age I would have thought he was too old to undertake long voyages
I'll keep you posted.