Here’s my translation
Hann bjó sik við þessum fundi frá því, sem aðrir menn.
He readied himself against (prepared himself for) this meeting (battle) from that [moment, point in time, (of that exchange)], as (ie like) the other persons (men).
Hann tók eina nautshúð hráblauta ok skar á rauf ok fór í ok gyrði at sér með reipi, eina öxi mikla í hendi, ok gekk út ok inn ok kvað:
He took one raw cow-hide and cut a hole in [it] and put it on (lit: went into [it], cf <fara I klæði>, Z18) and fastened a certain large axe (fem acc sg), in hand, to himself with a rope, and walked (stepped) out and in and declared:
Skalk með skjaldar runni,
I-shall with warriors (lit: shield’s-bushes (trees), acc. pl.) -
skapaðr erumk aldr, at gunni,
Lifetime (as in fate or destiny) is assigned (“shaped”) for me – to battle -
koma mun geira gjósta,
A battle (lit: a “gushing” (wind-gust) of spears) will come -
ganga fram sem Rósta.
go (step) forward, like Rósta.
Okkr þurfut nú,
Us (ie Guðmundr and Rósta) need-not (verb + enclitic neg. <at>) now,
þeirs oft á mik skella,
Those-who (<þeirs> = <þeir es (er)>) often scold (as distinct from scald 😊) me , -
sýnt munk seðja hrafna,
Clearly I-will satiate ravens -
saman of allt at jafna.
together always (see <of allt> under <of>, Z1) to compare.
[B] Skalk ganga fram með skjaldar runni at gunni sem Rósta. Skapaðr erumk aldr. Geira gjósta mun koma. Þurfut nú þeirs ella skella oft á mik, at jafna okkur saman of allt. Munk sýnt seðja hrafna.
I-shall go (step) forward with warriors (lit: shield’s-bushes (trees), acc. pl) to battle like Rósta. Lifetime (as in one´s destiny or fate) is assigned to me. A battle [lit: wind-gust (“gushing”) of spears] will come. Now, those-who (<þeirs> = <þeir es (er)>) often scold (as distinct from scald 😊) me otherwise, need-not to compare us (ie Guðmundr and Rósta) (together) always (see <of allt> under <of>, Z1). I-will clearly satiate ravens.
[C] Eg skal ganga fram með bardagamanninum í orrustunni eins og Rósta. Aldur minn er ákveðinn. Bardagi mun koma. Nú þurfa þeir ekki, sem kasta annars oft til min orði, að jafna okkur saman um alla hluti. Eg mun vissulega vega menn.
I shall go (step) forward with the-warriors into the-battle just-like Rósta. My lifetime (as in destiny or fate) is fixed. A battle will come. Now they, who address (lit: cast) a word (neut dat sg.) otherwise often to me (gen sg) (ie who often tell me the complete opposite), need not to compare us (ie Guðmundr and Rósta) (together) in all respects. I will certainly kill persons (men).
Þorvaldr kom á Eyri með hundrað manna, ok er hann sér viðrbúning Hrafns, bæði virkit ok fjölmenni mikit, þá sýndist honum óárenniligr bálkr þeira.
Þorvaldr came to Eyrr with a hundred (+ 20 perhaps) (of) persons (men), and when he sees [the] preparation of Hrafn, both the-stronghold and [the] great many persons (men), then their balk (partition, defensive barrier or set-up, nominative) seemed to him not easy to attack.
Síðan settist Þorvaldr niðr á brekku einni skammt frá virkinu.
After-that Þorvaldr sets-himself down on a certain slope a short-distance from the-stronghold.
Eyvindr Þórarinsson hafði safnat liði um Tálknafjörð ok Dali í Arnarfirði ok fór skipaliði til Eyrar.
Eyvindr Þórarinn’s-son had gathered troops throughout Tálnafjörðr and Dalr in Arnarfjörðr and journeyed by naval-force (lit: troop-of-ships, neut. dat. sg.) to Eyrr.
Nú er Þorvaldr sá, hvar skipin fóru, þá fór hann ofan til sjóvar með flokk sinn ok ætlaði at vera á ströndu fyrir, er þeir Eyvindr kæmi at landi.
Now when Þorvaldr saw, where the-ships journeyed, then he journeyed down to [the] sea with his body-of-men (party) and intended to be on [the] strand before (ie in advance of), when they Eyvindr [and co] would-come to land (ashore).
Eyvindr sá, hvar flokkrinn Þorvalds var í fjörunni fyrir.
Eyvindr saw, where the-body-of-men of Þorvaldr was on the-foreshore before (ie already, in advance of himself).
Hann mælti við sína förunauta, at þeir skyldi eigi at landi leggja skipin.
He spoke with his travelling-companions, that they should not land the-ships (lit: lay the-ships to land).
Þorvaldr kallaði á skipamennina ok spurði, hverr fyrir réði, en honum var sagt, at Eyvindr Þórarinsson réði fyrir.
Þorvaldr called to the-seamen (lit: persons of ships), and asked, who was-in-command but (and) to him [it] was said, that Eyvindr Þórarinn’s-son was-in-command.
Þorvaldr kallaði á Eyvind ok mælti, at hann skyldi leggja at landi skipin, — "því at ek vil tala við þik."
Þorvaldr called to Eyvind and spoke, that he should land the-ships (lit: lay the-ships to land), - “because I want to talk with you.’
Eyvindr svarar: "Ef þú átt nökkut vanmælt við mik, þá mæl þú þaðan, sem nú ertu kominn, en ek mun heðan svara, sem ek er kominn, því at ek á ekki vanmælt við þik."
Eyvindr answers: “If you have anything to say (lit: left-unsaid) with me, then speak-you from-there, where now you are (have) come, but (and) I will answer from-here, where I am (have) come, because I have not nothing to say (lit: left-unsaid) with you.”
Þá svaraði Þorvaldr engu.
Then Þorvaldr answered nothing
Þá sá þeir, er í virkinu váru, flokk Þorvalds ok skipamennina, hvar þeir kölluðust á.
Then those, who were in the-stronghold, saw the-body-of-men of Þorvaldr and the-seamen (lit: persons (men)-of-[the]-ships), where they called to each-other.
Í virkinu váru bræðr Eyvindar tveir, Tómas ok Halldórr, ok er þeir sá, hvar Eyvindr var kominn skipum sínum, þá ganga þeir ór virkinu með miklum flokki á móti Eyvindi, ok er Þorvaldr sá för þeira, þá gengr hann á braut ór fjörunni.
In the-stronghold were two brothers of Eyvindr, Tómas and Halldórr, and when they say, where Eyvindr was (had) come with his ships, then the walk out-of the-stronghold with a large body-of-men to a meeting with (ie to meet) Eyvindr, and when Þorvaldr saw their journey, then he walks away out-of the-foreshore.