I don't feel at all qualified to say much on this subject, Ive only been to Trethevy once and that was a few years ago, nor do I know a great deal about archaeology or arcaeoastronomy(just what ive seen on tv and in the few books ive been able to afford).
But some things I do know, if you stare long enough at something you will see what your looking for, in all aspects of life. You said in one post that you stayed on site for four days, and that the stones speak in a language were only now decoding, may I suggest that the lanuage being spoken is Gobbledy-gook and the message is gibberish, four days on site would be almost a torture, no wonder your beginning to see things in the stones.
Although ive been to Trethevy once, ive been to many other portal tombs, all over the place, and know one when I see one, and owing to a healthy interest in pyramids and dare I say it Atlantis, I know a pyramidiot when I here one. Of course we dont have pyramids (Silbury wont argue there) but it's never long before someone starts using stone circles or a burial chamber of some sort to make our ancient ancestors seem more incredible than they really were, Yes they did erect these wonderful monuments, and they may have encoded alignments into some of them, but they did so from a scared little animal point of view. Scared that they couldnt control everything around them, scared of what if anything came after our playtime here.
I'm sorry in the extreme if this sounds negative, but I dont hold a lot of faith in the extraordinary, no matter how hard I look for it the world stays obstinately ordinary, and I fear this will all blow over very quickly, like grinding corn on a trilithon.
Keep looking though, I am, just not too too hard