Thanks Moss, that's great. I've amended my post to include your findings too, if that's ok.
It is interesting how the king/giant/saint thing all gets a bit muddled up in many cases, isn't it.

There is a tma site for a Maen Llwyd nearish to that park, but it's not actually there? so maybe there's yet another stone in the vicinity...

Your trip to Wick sounds very interesting and I must go and see for myself. I remember the stones at the burial chamber being very red. You must put a link to your webpages on the lansdowns sites!
I'm off home now but will be mulling it all over..