Oh, oh, I am one of those two!
But as I never lost Amon Sûl its a bit hard to have an oppinion on the consequenses of an in- or destructable forge...?
Two sounds good in my ears, but it means that I myself will build it rather than it comes from/by an historic event, eh?
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From lore POV that seems far to great upgrades on the mines to me (se Gimlis comments under), as well as the logic of what a very small dwarven population would be able to muster no matter the financial backing they get, just as a note;
[Legolas:] "Maybe the men of this land are wise to say little: one family of busy dwarves with hammer and chisel might mar more than they made."
"No, you do not understand," said Gimli.
"No dwarf could be unmoved by such loveliness. None of Durin's race would mine those caves for stones or ore, not if diamonds and gold could be got there. Do you cut down groves of blossoming trees in the springtime for firewood?
We would tend these glades of flowering stone, not quarry them. With cautious skill, tap by tap -- a small chip of rock and no more, perhaps, in a whole anxious day -- so we would work, and as the years went by, we should open up new ways, and display far chambers that are still dark, glimpsed only as a void beyond fissures in the rock."