Ocifant - regarding Watchcroft: how about contacting Ian McNeil Cooke who wrote that excellent book 'Mermaid to Merrymaid - Journey to the Stones'? (You've probably already got a copy.) He used to live at Men an Tol Studio, I think.
My book is a 2000 reprint and inside the cover it gives an address: 'Men an Tol Studio, Bosullow, Penzance, Cornwall, TR20 8NR. (I was going to add the phone number here, but maybe that's not wise. It's probably changed anyway since then.)
Turning it out has reminded me what a great book it is, and shall have to try and find time to read it properly!
(Do you remember meeting my friend Angela and me - [I was the quiet one, dowsing!] - at Boscawen Un in 2004? I emailed you afterwards about that strange Creeg Tol site near there.
Good luck. (Hope the knees improve.)