Meini Gwyr has been almost entirely demolished over the centuries, the last two combining to cause more damage than the previous thirty or forty (but that is so often the case) the notice board at the gate describes the state of the site a couple of hundred years ago with a henge, combined with a circle of large stones, and an entrance-way of more than usual complexity, consisting of a stone-lined passage through the earth bank. Here is a sketch made by William Stukeley of the site.
All that now remains is two stones and the merest suggestion of the earth bank circle. Two fields away two VERY large stones can be seen, outliers of who knows what purpose. They are the ones noted in the comment by Stukeley at the bottom of the sketch. From the map they can be seen to be toward the west but whether there is some significant alignment to the vernal equinox sunset (or some other) I can't say. I shall spend my dotage with a theodolite investigating any that Thom and Burl have left for me.