... this would suggest that Harlindon is roughly where Ossiriand is and Forlindon is where Thargelion is. Of course, I could be wrong, and I'm not 100% cirtain of this interpretaion.
Well, I'm not 100% sure of mine either - as I said, it's difficult to determine.
The shape of the Ered Luin on the two maps tends to support your theory (indeed the theory I ascribed to for quite a while). The direction of the East-West Road through the Shire also may point to Belegost and Nogrod being 'under' the Gulf of Lune.
Looking at the maps in the Silmarillion and UT, I'd have thought that the Gulf of Lhun was about where Belegost was (wasn't Belegost destroyed at the end of the First Age wen Beleriand sunk?)...
The Tale of the Years relates for "c. 40SA" that "...Dwarves, leaving their old cities in the Ered Luin...". What old cities are not stated. They are either un-named and unmentioned cities, in which case they could be in any part of the Ered Luin (or anywhere else), or they are the only named cities of the Ered Luin, ie Nogrod and Belegost. If they were Nogrod and Belegost, then those cities weren't destroyed and sunk 40 years previously.
... Looking at the maps, Himring is roughly in line with a spur of mountains/hills that come off the main chain of Ered Luin, as is it's Third Age counterpart Himling...
Yes, this is Mount Rerir that I mentioned in my earlier post. According to the map in UT, the distance from the middle of the island of Himling to the point where the Mount Rerir spur diverges from the main chain is around 150 miles. The distance from the point of divergence to the middle of the Gulf of Lune is around 300 miles - in other words, the Gulf of Lune is twice as far from the Mount Rerir spur as Himling is.
If we look at the Silmarillion map, and apply the same scheme (measure the distance from the Mt Rerir spur to Himring, then double it for the Gulf of Lune), that would put the Gulf of Lune where the River Duilwen is, in the south of Ossiriand.
In other words, Nogrod and Belegost are about the same distance south of the Mt Rerir spur as Himring is west of it; so find the distance fom the spur to Himling on the Unfinished Tales map, and head the same distance south to find Nogrod and Belegost.
Nogrod and Belegost, under Mt Dolmed, would on this reckoning be on the Unfinished Tales map where the double-peaked mountain stands out to the west of the main range, slightly south of where the river of Forlindon flows down, at the top of the central/southern range of woods.
This would allow them to not be underwater and the Dwarves to continue living there for another 40 years.
It would also mean that Beleriand is only about half the size we think it is, and attached to Forlindon but not necessarily Harlindon.
But, as I've said, it's difficult. Neither explaination is entirely convincing. The Dwarf cities might
be different cities. The East-West Road might
kink north. The position of Himling might
be wrong. The line of the hills might
be out on the map.
I trust the position of Himling but not the line of the hills. If you trust the line of the hills, that's fine, but Himling's in the wrong place. I trust that the entry refers to Nogrod and Belegost, not un-named other cities, and think the road turns. But that's just about plausability not fact. "Other interpretations are possible".