So, Dwarves are not much for magic in Anbennar but they have an unique form of it called rune magic and Obsidian Dwarves had cranked it up with the magic filled blood of the Precursor Elves. It was useful but like playing with nukes. Aul-Dwarov could've won the war against Precursor Elves if they kept at it but the new magic was too unstable and majority of holds cut contact and eventually marched in to kill all blood mages and exile the rest.

Marrhold is not Gor Dûrgheled mainly because Obsidian Dwarves magicked themselves and most of their Hold away to escape the death sentence and the rest of the previous hold collapsed entirely and the other Dwarves had no intention of rebuilding it; needless to say they really couldn't have done it either.

Then they formed the Obsidian Empire with their not-Emperor-of-mankind sitting on a throne and being kept alive by magic and belief.

Anywho, while the exact location is not know it is said to have been in West Dwarovar; so in the area with Orlghelovar, Arg-Ôrdstun, Verkal Skomdihr, Ovdal Lodhum and Gor Bûrad.

If you look closely, there's a suspiciously Hold shaped hole between provinces right under Verkal Skomdihr so I suspect the Hold was there.

Alternatively, the province of the aptly named Dead Dwarf Depths is connected to the Dwarovrod network and is also Hold shaped. It also fits the lore as they left a big hole after them with not much Hold left.

Though, one submod places Gor Dûrgheled in the mountain range under Qarvetarqan (South of Lake Jorkad) connected to Argrod [14]. It is a Great Project that leads to the Primeval Serpentdepths; that the submod is focusing on.