[Findegil]

1. Oarni: I have look that up in the Quenya lexicon but it did not add any information to the entry in the Appendix of LT1 given by Maédhros.
I agree to change it to Earni if we keep it. As said before I see more evidence that such "fantastic" elements could be kept that for deleting the Earni. So I vote for keeping them in. If we later discover any reason against that we could still come back to the case and work on the passage again.
So we agree upon this point.

2. The Horns of Ylmir: I am strongly inclined against your possibility 2. I think we have either to move the poem to the editorial appendix or to edit it so that we are at least satisfied with the complete result and I can't see how we can do that is we lose the intro.
Your emendations are not so bad. When we first discussed the idea I tried to do the same my self, but I came not very fare with it. I will provide the thoughts that I had:
Line 1:

{'Twas} [Here] in the Land of Willows where the grass is long and green −

"Here" does not alliterate with the line. I am not sure if that is needed, but I thought it would be nice to alliterate. I thought of

{'Twas} [I wander] in the Land of Willows where the grass is long and green −

Since that adds some new meaning it is to risky.
Line 2:

I {was} [sit] fingering my harp-strings, for a wind {had} [has] crept unseen

That was the line I have get no solution for that was good. But following your example and my line 1 I would think that "walk" will go. I was not sure if we should change the second half-line at all. We can assume that the wind had already crept and inspired the Song and stopped when the poem is made.

I {was} [walk] fingering my harp-strings, for a wind had crept unseen

Line 3 & 4:

And {was} [is] speaking in the tree-tops, while the voices of the reeds
{Were} [are] whispering reedy whispers as the sunset {touched} [hits] the meads,

At least we should right the "are" as "Are" since it is the start of the line. As said before I think we could leave the wind in past tense.

And was speaking in the tree-tops, while the voices of the reeds
Were whispering reedy whispers as the sunset touched the meads,

Line 5:

{Inland musics subtly magic} [But my heart recalleth sea musics] that {those} [the] {reeds} [waves] alone {could} [can] weave −}

That is the hard part as you said. Your line is good in it self. But it is as if you swept of the old one and made a new. I have no better solution but I am not sure if we could not bear the break if this line is unchanged from the original?
Line 6:

It was in the Land of {Willows} [Nevrast] that once {Ylmir} [Ulmo] came at eve.

We cannot avoid to change that line. So I think we should make the transition here if possible. My solution is not good, and can do not much more than illustrating the idea.

{It was}[I wander] in the Land of Willows {recalling} that once {Ylmir} [Ulmo] came at eve.

I hope this will not be the best we can get, other wise I think we have to delete the poem form the main text. But may be it will stir some better ideas.

Respectfully
Findegil