"The symbols that most often occur side by side with the S&XB are the hour-glass, the bell and the coffin. The symbolism is pretty clear."

Yep, I think so. I still see it as part of the Dance of Death tradition (the Danse Macabre was often carved on church walls). Death was much more of a presence in the lives of medieval people than it (he?) is in our lives, and their art/symbols show a preoccupation with, indeed, almost a celebration of, death.

Like I say, though, well off topic. I could talk about the Danse Macabre all day, but I think I'd better be quiet now. :)

A recurring theme - some of the Pewsey stones have holes through/in them and so does at least one of the Alton Priors' stones (as must many more stones at many other sites). Why?

For a fascinating discussion of "... man's eternal conflict with the forces of good and evil." see The King and the Corpse by Heinrich Zimmer. Princeton University Press; ISBN 0-691-01776-X.