The Demon Of Scattery show vikings routinely wearing horned helmets. However, see here. Also, I attended an educational dramatic performance in Lancaster where an actor wearing a horned helmet informed us that such helmets were originally worn only on ceremonial occasions.
Halldor reflects on Norwegian accounts of "Whatever lay beyond..." (p. 22):
feasts in god-halls;
gloom in the underworld;
half-life in the grave;
"...and who knew how much else?" (pp. 22-23)
Here, the authors acknowledge that much is unknown about ancient beliefs. Thus, Halldor's memory of whatever else he has heard fails just at the point where modern knowledge of preliterate and pre-Christian beliefs reaches its limit.
The besieged abbot addresses Halldor as "'...Lochlannach...'" (p. 21) (see also here) and claims to be a successor of Saint Senan.
"...Brigit prayed. 'Our Father...' But when she closed her eyes, instead of God she saw only Conaill, her earthly father." (p. 32)
But what would God have looked like?
"Her dreams were jumbled: God the Father, Conaill, and Halldor wore the same countenance." (p. 38)
But did she have a usual image of God's countenance? I remember reflecting that I knew what the Son looked like but not the Father and thought that this was only because I had not yet seen a picture of the latter. A picture of the (human) Founder of a Catholic religious order hung in the hallway of a school. I wondered if that was the Father and found that I did not like the way he looked. Of course, pictures of the Father as a bearded man are common in European religious art, e.g., in the Sistine Chapel. Such representations contradict the New Testament idea that the Father is seen only in the Son.