Nothing doing here with any pictures either. I haven't been that way in a long time and when I was there it was under heavy mist.

I just looked back at Somerville's plan and his line runs from the centre of the axial through the right portal and seems plausible.
Patrick and Freeman surveyed a number of circles years ago and looked at data from both sides, that is the line between portals to centre axial and the line between centre axial through portals, and found a much stronger, though admittedly rough and occasional, solar event orientation to the southwest.

Their survey of Derreenatagart threw up a declination from the portals through the axial of +7.76degrees and one in the opposite direction of -4.15degrees.
For whatever reason Ruggles, when he surveyed the portals to centre axial, found it to be significantly different at +4.2degrees.

None of these results are unfortunately anywhere close to an accurate equinox sunset orientation. Tiompan may be able to correct me on this but I think the declination for that event is +0.5degrees.

The closest circles to the bullseye are apparently:
Dromroe +1.2 (Ruggles), +0.83 (Patrick)
Bohonagh +0.6 (Ruggles), +0.88 (Patrick)
Knocks North +1.22 (Patrick)
Cappanaboul +0.6 (Ruggles)

Good luck and fine weather for the hunt,
g.