Simon James

For a change, here's a "mystery that has me mystified" that I might have solved. The 1978 novelisation of the Western Across the Great Divide from Arrow Books was published under the byline Simon James, which I suspect might be a pen-name. But for whom? Well, the one clue in the book is the dedication "To Ysanne, Simon and Barnaby". Ysanne is an uncommon name and, I thought, worth a Google