[Maédhros]

FG-A-01
Now when the {seventh} summer [of the treason of Maeglin] had gone {since the treason of {Meglin} [Maeglin]},
In all chronologies from the "The Earliest Annals of Beleriand" to the last version of "The Tale of Years" Maeglin's treachery occurs the year before the fall of Gondolin, not seven years and and some months before its fall as in FG. I have slightly changed a phrase and moved its position to create the required new information.

I think that this could help with the problem of the Balrogs.

There too were the folk of the Pillar and of the Tower of Snow, and both these kindreds were marshalled by Penlod, tallest of Gnomes.

Was this addressed at some point before? This certainly conflicts with the account that Turgons was the tallest of the elves save Thingol.

FG-D-01 Deleting from Maeglin's advice to Morgoth.
{From the greatness of his wealth of metals and his powers of fire he }[He] bid him make {beasts like} snakes and dragons of irresistible might that should overcreep the Encircling Hills and lap that plain and its fair city in flame and death.
Maeglin now advises Morogth to make snakes and dragons (by which should be understood more of the normal kinds of snakes and dragons) but of great strength, as the best means of bringing Gondolin to the ground.

I'm of the idea of replacing the "Mechanical Monsters" with dragons. One of the problems that I had was that why would Melkor had to wait 7 years for the "creation" of dragons. I do not know the time it takes to breed one but i bet that it's longer than 7 years. But because in the new account only 1 year passed, it could be said that Maeglin advised Melkor to use dragons and snakes (?) that he already had. The lapse of 1 year can be attributted to the fact that it takes time to move such an army.

Then on a time {Melko} [Morgoth] assembled all his most cunning {smiths and} sorcerers, and {of iron and flame} they wrought a host of monsters such as have only at that time been seen and shall not again be till the Great End.

Agree with this.

yet others were creatures of pure flame that writhed like ropes of molten metal, and they brought to ruin whatever fabric they came nigh, and iron and stone melted before them and became as water, and upon them rode the Balrogs in hundreds; and these were the most dire of all those monsters which Melko devised against Gondolin.

Is the concept of fire drake acceptable or are they just dragons. I would modify it this way:
yet others were [dragons] (perhaps those like Glaurung's kind)of pure flame that writhed like ropes of molten metal, and they brought to ruin whatever fabric they came nigh, and iron and stone melted before them and became as water and [with] them came balrogs; and those were the most dire of all those monsters which Melkor [used] against Gondolin.

And thus it was that the fire-serpents of Melko came upon Gondolin.

And thus it was that the [dragons] of Melkor came upon Gondolin.

and the love of Tuor and herself that had dwelt therein; but now she saw its destroying nigh at hand, and feared that her contriving would fail against this overwhelming might of the terror of the serpents.

Again, I think that serpents can be changed to dragons.

It was now four hours still from middle night, and the sky was red in the north and in the east and west; and those serpents of iron had reached the levels of Tumladin

dragons of iron scales as suggested elsewhere.

Then the engines and the catapults of the king poured darts and boulders and molten metals on those ruthless beasts

engines?

an innumerable host of the {Orcs} [Orks], the goblins of hatred,

globlins of hatred? I know that the term is used in the Hobbit, but is it appropiate here?

He seized Meglin by that hand that held the knife and broke the arm with the wrench

wrench?

yet a worse matter was it that {a company} [one] of those demons climbed upon the coils of the serpents of iron and thence loosed unceasingly from {their bows and slings} [his bow] till a fire began to burn in the city to the back of the main army of the defenders.

I can live with this but a balrog with a bow?
I would have used instead a hosts of orcs with bows. I can't imagine a balrog with a bow.

But now the men of Melko have assembled their forces

Men? I would replace by, now the host of Melko was assembled.

Then leapt Ecthelion lord of the Fountain, fairest of the Noldoli

Is Echtelion to remain the fairest of the Noldor?