Yardley's book is indeed good, but I've reading another that, IMO, is the finest one written on the subject. It is Stock Fitter's Bible by Rollin Oswald. it was recommended to me by a forum member here. It is a treasure trove explaining all shotgun stock dimensions, how and why they affect shot placement like they do.
I wish I had found this book 30 years ago., but I don't think it had been written at that time. I believe you would greatly enjoy it, Chuck. It's that kind of book I keep a pen in, so that I can underline stuff for future reference. Covers all different shotgun disciplines, not just trap and skeet. Much space is given to sporting shooters.