I can find no OTHER reference to this location anywhere. There are six "normal" Trolls here.
It appears that this location/Quest might have existed in the past in the moors, as this troll cave is adjacent to the third entrance to the Isendeep Mine, right on the border between Arador's end and the Steps of Gram.
However, the Trolls there don't agro unless you provoke them. And it appears to only be a "short, straight" cave. I can find no evidence of it linking to anything else.
Also, the "Radar" shows it to be in the Steps of Gram -- 12.0S|19.3W
If this truly is the quest Instance related to "Troll Height," it does not belong in the Moors.
There is a solo instance: "The House of Isldur" (which takes place in Forochel) in the Epic quest string -- Volume III Book II Chapter 3.
This Troll-height is the NEW Troll-height. The OLD Troll-height is now called Arador's End after the end of Arador, Chieftain of the Dúnedain in the year 2956 of the Third Age, at the hands of the trolls there.
Trolls has been spelled 'Tolls' in this page. However, it is protected and I cannot correct it.