Yikes, I'm getting a bit behind.
> Þorkell mælti svo að sá væri engi á Íslandi að hann mundi eigi ganga
til einvígis við eða á hæl (hæll) hopa fyrir.
> Þorkell spoke so that that-one (person) was no-one in Iceland that
he would not go to (engage in) in single-combat with or draw-back
before on (his) heels (recede before) (see hæll, hopa á hæl fyrir e-m)
This is another example of the demonstrative pronoun being used in an
indefinite sense: "Þorkell declared that there was no one in Iceland
he wouldn't fight a duel with or [would] retreat from."
> Ásgrímur þagnaði þá og þótti þungt fyrir.
> Ásgrím became-silent then and (it) seemed heavily for (?).
'þungt' "gloomy" is the way he's feeling. "A. became silent and felt
glum [about the situation, their hopes of support]." The dative would
be used for the experiencer (honum var þungt; honum þótti...), but
here the pronoun is left out juts as we can leave out the equivalent
nominative pronoun in "A. fell silent and [he] felt glum."
> Og þegar er eg næ til þín skal eg reka það í gegnum þig
"when I reach you"
'næ' = present indicative 1st person singular of 'ná' "to get/obtain,
reach, manage to".
> ljósverk
Re. MM & HP's "milking cows", see 'ljósa-verk' here [
http://lexicon.ff.cuni.cz/png/oi_cleasbyvigfusson/b0395.png ]. They
interpret it as derived from the "light" colour of the milk (and dairy
products), hvítr matr. I wonder if Skarphéðinn is making a play on the
name 'Ljósvatn'?
> Hann mælti: "Búið arki að auðnu til hvers sem draga vill."
'bú(i)ð' + subjunctive = "perhaps" [
http://runeberg.org/anf/1883/0348.html ], short for 'við búið' / 'við
búit'. In reference to another example in Njála, 'ok búð ek láta
annars víti at varnaði', the Proverbs page quotes the ÍF edition "búð
= má vera at. Orðið búð er dregið saman úr búið (svo R í 120. kap.),
eldra búit, og merkir: við búið" [
http://www.usask.ca/english/icelanders/proverbs_BNS.html ].
The -i in 'arki' is the subjunctive 3rd person singular, used in an
impersonal sense: "it will trudge/go towards fate". There's a literal
translation here: "According to destiny probably [it] may go to
wherever [it] will pull" [
http://philologia.jp/pdf/xi1.pdf ], where
"probably" = 'búið'.