Click here for a recording of me speaking the words of the St Magnus hymn. This is just here as a guide to pronunciation.
I've gone for a sort of generic medieval Latin pronunciation; it's hard to know exactly how this would have been pronounced in Orkney, as there were marked local variations as well as changes over time, and of course even the scholars can only make an informed guess, since there are no recordings! But this may well differ from the pronunciation you might have been taught as "Church Latin", because that's really late nineteenth-century Italian pronunciation ...