Hi Bladup!
The 6-figure grid ref is good. Can U tell us the letters preceeding it (it'll be on your map). Izzit, e.g., NZ 666 777, or SD 666 777, SE ...... The first coupla letters will help us out big-time! Find 'em, tell us, & we'll find y' standing stone!
Cheers (v. ASC-ed) - Paulus