Here’s my translation

Alan

Sá atburðr varð undir virkinu, þar sem ljósit hafði sézt um vetrinn áðr. 
That event (or attack, <atburðr>, Z1 or 4) happened under the-stronghold, there where the-burning-light had been-seen the-winter before.

Þar var þá leir, er Hrafn var höggvinn, en um sumarit eftir var þar grænn völlr.  
There was then mud, where Hrafn was beheaded, but during the-summer after a green field was there.

Þorvaldr lét höggva fót undan Sturlu Bárðarsyni ok Þórði Vífilssyni. 
Þorvaldr caused to hew (smite) a leg (with foot attached) from-under Sturla Bárðr’s-son and Þórðr Vífill’s-son.

Þessir atburðir urðu annan dag viku í annarri viku langaföstu, átta nóttum eftir Matthíasmessu. 
These events happened on the second day of [the] week in [the] second week of Lent [lit: Long-Fast), eight nights after Matthíasmessa (St. Matthew’s Mass)

Þá rænti Þorvaldr bæinn á Eyri öllu lausafé, því er innan veggja var, vápnum ok klæðum, húsbúnaði, búsgagni ok mat. 
Then Þorvaldr plundered the-farm at Eyrr of all movable-property, that which was within [the] walls, weapons and clothes, house-furnishings, household-utensils and food.

Í því ráni tóku þeir sólarstein góðan ok kyrtil brúnaðan með búnaði. 
In that plundering, they took a good lode-stone and a dark-coloured kirtle with ornaments (<búnaðr>, Z4 = <búningr>, Z4)

Þá gripi hafði Guðmundr byskup átta ok gefit Hrafni. 
Bishop Guðmundr had owned those treasures (ie the ornaments) and given [them] to Hrafn.

Þeir tóku ferju eina, er kirkjan átti, ok báru þar á þann fjárhlut, er þeir ræntu. 
They took a ferry-boat, one which the-church owned, and bore there-on that property, which they plundered.

Ok er þeir váru á braut farnir með skipit ok fjárhlutinn, þá fundu heimamenn á Eyri sólarsteininn þar, er þeir höfðu eykinn búit, því at þeir höfðu honum í brott kastat ok kölluðu vera hégetil. 
And when they were (had) journeyed away with the-ship and the-property, then [the] household-folk at Eyrr found the-lodestone there, where they had made-ready the-ferry-boat (presumably <eykr> = <eikja>, where a ´beast of draught’ = ‘a ferry-boat’, the ‘draught’ in this case being ‘the depth of water needed for a boat to be able to float’ 😊 -otherwise probably simply a scribal error, see CV) because they had cast it away and called [it] to be (ie mistakenly regarded it as) flint (<hégeitill>).

Svá ok kyrtilinn höfðu þeir eftir látit ok kölluðu vera vaðmálsslopp, ok eigi fengu þeir sét á búninginn. 
Also they had left (<láta>, Z3) the-kirtle behind (<eptir>, Z.iii.2) and called [it] to be (ie mistakenly regarded it as) a wadmal-gown (for a priest), and they were-not-able (fá + pp, Z7) to behold (ie they overlooked) the-ornaments.

Þenna atburð virðu menn svá, at því mætti þeir þessa gripi eigi í brott hafa, er Guðmundr byskup hafði átt. 
Persons (men) assigned a value to this occurrence (or gesture, <atburðr>, Z1 or 4) such, that for that (reason) they might not (ie would not be permitted to, <mega>, Z2) take (<hafa>, Z7) these treasures away, which Bishop Guðmundr had owned.

Þat vár it sama fór Þorvaldr eftir páska í annat sinn í Arnarfjörð ok rænti þá marga þingmenn Hrafns. 
That spring, the same (one), Þorvaldr journeyed after Easter a second time to Arnarfjörðr and plundered those many liegemen (‘Thing-men’) (as <marga> is weak, I think <þá> must be a dem. art.) of Hrafn.

Pétr Bárðarson lét drepa þingmann Þorvalds, þann er Hermundr hét. 
Pétr Bárðr’s-son caused to kill that liegeman of Þorvaldr, who was-called Hermundr.

Sá hafði verit í andskotaflokki við Hrafn. 
That-one (ie He) had been in [the] band of adversaries against Hrafn.

Þorvaldr sendi orð Kár munki Geirmundarsyni, at hann skyldi leita um sættir við frændr Hrafns. 
Þorvaldr sent word to Kárr [the] monk Geirmundr’-son, that he should try-to-effect agreements with [the] kinsmen of Hrafn.

Þá var settr sáttarfundr þessa málaferla at ráði Þórðar Sturlusonar ok Kárs munks á Þingeyri í Dýrafirði. 
Then was set a peace-meeting of these law-suits (gram plural) by [the] advice of Þórðr Sturla’s-son and Kárr [the] monk at Þingeyri (place-name, I was there briefly in 1999) in Dýrafjörðr.

Þá var sætzt á þessi mál á þann veg, at Þórðr Sturluson skyldi gera um þessi mál öll, þann veg sem hann vildi. 
Then [it] was come-to-terms in these cases (plural) in that way, that Þórðr Sturla’s-son should arbitrate in all these cases, that way as he wanted.

Tólf menn handsöluðu fyrir Þorvald fégjöld, svá sem Þórðr vildi gera, ok til þeirar sýknu Þorvalds, sem Þórðr vildi vera láta. 
Twelve persons (men) made-over-by-handshake fines (plural) for Þorvaldr, such as Þórðr wanted to assign, and to that acquittal (declaration of innocence, presumably variant of  <sykna>, Z1) of Þorvaldr, which Þórðr wanted to cause to be.