[Maédhros]

Aiwendil I'm in favor of all of your emendations except for this one:
line 5:

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

Can you explain to me why can we not use Squatter emendation of that line:

'Ocean musics subtly magic that those waves alone could weave'

Then we would have:

{'Twas} [Here] in the Land of Willows where the grass is long and green
I {was} [sit] fingering my harp-strings, for a wind {had} [has] crept unseen
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,
'Ocean musics subtly magic that those waves alone could weave'
It was in the Land of {Willows} [Nevrast] that once {Ylmir} [Ulmo] came at eve.

I will check the rest of the poem later.