> laust (ljósta)

You're right, and I was wrong!

http://www.septentrionalia.net/lex/index2.php?book=e&page=380&ext=png

That gives us: "Thor drove Thangbrand's long beast of Thvinnil (=ship)
off course, shook and bashed the box tree of the prow (=ship) and
STRUCK it against the land."

> Þór brá Þvinnils dýri
> Þangbrands úr stað löngu (adv?),

> Þor impelled (drove) (the) beast of Þvinnil (ie ship)
> of Þangbrand out-of place long-ago,

'löngu' is a dat. sg. neut. adjective (langr) agreeing with 'dýri',
hence "long ship", rather than being part of the phrase 'fyrir löngu'
"long ago".

http://www.septentrionalia.net/lex/index2.php?book=e&page=358&ext=png

> búss
> (box-tree – but can´t find in any dictionary, mast?)

Lex. Poet. just has "a type of tree". Faulkes, in the glossary to his
edition of Skáldskaparmál, has "box (tree)". Here it's used loosely as
a part of a kenning for the whole "ship": 'búss barðs' "wooden thing
of prow, wooden thing characterised by having a prow". It's the same
idea as the kenning 'skíð grundar Atals' "ski of Atal's field/ground",
and makes use of the principle of substituting one wooden object for
another, as happens in kennings for "man" or "woman" where any tree
name or wooden thing of the appropriate gender can be used as the
base-word. In fact, Snorri cites the example 'regg-búss' "ship-tree"
as a kenning for "man".

http://www.septentrionalia.net/lex/index2.php?book=e&page=71&ext=png

> hregg
> (the) storm

Yes. 'hregg ... hánum kennt' "the storm attributed to him".

> Þór drove Þangbrand's ship (beast of Þvinnil) from (its) spot (off

course, from its anchorage?) [...]

I'm not sure what precisely it's saying that his ship is driven away
from. I assumed it was it's course, but maybe it was ancored at the
time. The prose suggests that it was wrecked in the course of his
travels. Does 'braut austur við Búlandsnes' perhaps imply that it was
out at sea, at least, rather than in a sheltered anchorage?

> dashed (it, ie the ship) against (the) earth (shore?).

Yes, earth = land = shore.

> harshly began to lay (it, ie the ship) into pieces.

In poetry, auxiliary verbs like 'taka', 'gera', 'nema' can be
superfluous to the meaning, like 'do' in traditional English verse. I
think that's covered everything. Let me know if I missed anything. And
thanks for clearing up 'laust' for me! That makes more sense now (as
well as agreeing with the experts...).