The current angle of the hole realtive to the capstone plane/vertical may be misleading as there is great speculation regarding the original attitude of the capstone. Presently, the capstone sits neatly on the side stones, but when the height of the fallen backstone is considered, it could never have fitted beneath the rear of the capstone at the present angle]

Well by what I could see the attitude looks correct to me when you consider the top angle of the very wide upright at the rear right looking from the 'front' of the dolmen. The cut/angle of it must be 4ft long and the capstone fits it perfectly. As for the fallen backstone, well when it originally fell inwards it would have risen out of the ground somewhat as it levered itself against the top of the socket it would have originally stood in, so would show more above ground then normal.

[There is quite a flaring of the hole on the underside of the capstone, and this very pronounced on the "rear" side which would fit with weathering]

Agreed, but it would also fit with the hole needing to be vertical and by doing this the rear would naturally have more removed leaving it as it is today

[We noticed five depressions in the back of the rear stone that may be drill holes, plus two really deep ones in the side of the surviving flanking stone]

Yes I noticed them as well and photographed them all. Altogether a lovely site to visit and I have to say that on every occasion I have been there I have been alone. Then again, if you turn up with a 20ft pole and act like an idiot it's probably just as well.