The 'Alfred' manifest arriving, as you have, in Sept 1858 shows a Robert Black, aged 21, a ploughman by occupation and originating from Stirling. Have you tried to follow up details with that info back in the earlier Scottish censuses. There is this one for example from 1851:
Robert Black, 15, farm servant b. Stirling. This entry shows at the farm of a John Blair, at Little Ward, Kincardine, Perthshire....can't easily connect to an 1841 census entry so far.
Monica
MonicaL thanks this is a good lead no hook