Here’s my translation

Alan

Því næst bað Sigrgarðr þau vel lifa. 
In the-next (moment) (ie thereupon), Sigrgarðr bade them (ie Gustólfr and Gerðr) to live well.

Kerling fekk honum einn posa; sagði honum hversu hann skyldi með fara þat sem í var ef til þyrfti at taka. 
(The) old-woman gave him a certain little-bag; (she) said to him how he should go (proceed) with that which was in it (ie make use of its contents) if (he) needed to have-recourse to (it) (taka til e-s, Z12)

Hon bað hann veita tveimr mönnum fari í skipi sínu þó at ei væri merkiligir ok hafa ráð þeira um þá hluti sem honum þætti miklu máli varða. 
She bade him to grant two persons (men) passage in his ship even-though (they) would-be not remarkable and to have (ie accept) their advice about those things which seemed to him to warrant a great matter (ie which were of great importance, mál, Z11).

Fór Sigrgarðr í burtu. 
Sigrgarðr journeyed away.

Báðu þau vel fyrir honum.
They prayed well for him (ie for his well-being) (biðja fyrir e-m, Z1).

Sigldu þeir nú austr fyrir Tartararíki. 
They sailed now east for (the) kingdom of the Tartars (ie Tartaría)

Einn dag sigldu þeir mikit veðr ok urðu nærri björgum nökkurum. 
One day they sailed in a great wind (or heavy weather) and became near (nærri = nær) some cliffs (bjarg)

Maðr kom fram á bjargit. 
A person (man) came forth onto the cliff.

Hann var mikill vexti ok undarliga skaptr. 
He was large in stature and extraordinarily strong / minded / shaped (skarptr? Or ‘minded’, skaptr, CV? Or ‘shaped’ contraction of skapaðr, pp of skapa or strong form of pp of skapa? Looks like Hall has ‘shaped’ -based on what follows this seems the most likely meaning)

Hann hafði kring mikinn ok var í gráum veipustakki. 
He had a great ‘roundness’ (bulge? cf kring, CV?) and was in grey cape (short cloak)-with-wimple (veipa).

Þat bar þó meir við hversu þjóabrattr er hann var, því var líkast sem klæðsekkr væri laginn um þverar lendar honum ok tók ofan í knésbót. 
That passed still further beyond (bera við, Z.ii.2?) howsoever (hversu…er?) butt-steep (þjó, brattr, adj) he (the man) was (ie I think this is saying the cloak extended below his butt, despite his butt projecting out so far), because (it) was most-like as (if) a clothes-bag was (ie had been) laid across his rump (lend) and (one) pulled (it) down (taka ofan, Z12) into (the) hollow-of-the-knee.

Hann beiddist fars. 
He (ie the man with the big butt) requested-for-himself passage.

Sigrgarðr spurði hvat honum væri til lista gefit en hann kveðst vel aka segli. 
Sigrgarð asked what was given to him for skills (ie what skills had he been endowed with) but (and) he declared-of-himself to trim a sail well.

Hann bað hann hafa skip ef hann næði. 
He (Sigrgarðr) bade him to have (ie join) the ship if he could-reach (it).

Hinn stökk af berginu ok út á skipit, ok gekk skipit niðr um nagla. 
That-other-one (‘big butt’) leapt from the-cliff and out on to the-ship, and the-ship went down beyond (um, Z.i.4) (the) nails (spikes, nagli).

Þetta hlaup var þréttán álna af landi. 
This leap was thirteen ells from land.

Hann greip í aktauma ok dreif þegar skipit frá landi. 
He caught-hold-of the sail-braces and drove at-once the-ship from (the) land

Þeir spurðu hann at nafni. 
They asked him as regards (his) name.

Hann kveðst Hörðr heita ok vera kallaðr harðstjölr. 
He declared-of-himself to-be-called Hörðr and to be called ‘hard-butt’

Þeir hlógu at honum.
They laughed at him.

Annan níunda dag eptir sigldu þeir enn með landi fram. 
On (the) ninth day following (annan, Z3) they still sailed forth (fram) along (the) land

Þar var útgrynni mikit. 
There was a great shallowness-stretching-out-from-the-shore (shoal).

Þar stóð maðr á landi. 
There stood a person (man) on land

Sá beiddi fars, hann var hár vexti ok í vargskinns stakki. 
That-one (He) bade passage, he was tall in stature and in a cloak of wolf-skin.

Sigrgarðr spurði þann at nafni. 
Sigrgarðr asked that-one (ie him) as regards (his) name.

Hann sagðist heita Velstígandi. 
He said-of-himself to be-called Velstígandi (Stepping-well)

Sigrgarðr spurði hvað honum væri til lista gefit, en hann kveðst troða vel marvað. 
Sigrgarð asked what was given to him for skills (ie what skills had he been endowed with), but (and) he declared-of-himself to tread sea-wading-places (sea shoals, mar + vað, cf marvaði, CV) well

Hann kvað þat góða íþrótt, ok bað hann troða til skips ef hann villdi farit fá. 
He declared that a good skill and bade him to tread to (the) ship) if he wanted to get the-passage.

Hann sté út á sæinn; alda var mikil en þó rann hann til skipsins ok tók honum aldrei upp yfir skó, ok mundi þat vera sex tigu faðma frá landi. 
He stepped out on to the-sea; (the) swelling-wave was large but (and) still he ran toward the-ship and (it, the water) never took (ie reached) up over his shoe, and that would be sixty fathoms from land.

Þessi maðr hafði króksviðu i hendi.
This person (man) had curved-cutlass (krókr + sviða, ‘hatchet with a hook’, CV) in hand.