Hi Peter,
placement of upper attachment of Diamond wires I have always just looked at where the stays will clear them when mast is rotated. Markings on old mast may give you a good guide, if Hound and Diamond wire fitting to mast use the same method.
As a matter of interest I have heard people say that getting them as close to the hound fitting as possible, is one of the reasons for using T ball terminals. As they are generaly lower profile than any other method I have seen.
I have always placed spreaders in the middle of the diamond wire attachment points, don't know why just seemed right. I haven't heard any reason for doing it any other way.
Along with my own masts I have helped Tim, Peter and Neil build masts. Having a swaging tool and large riveter I tend to attract these jobs. Pity you are not closer.
Regards Gary. <img src="http://www.catsailor.com/forums/images/graemlins/tongue.gif" alt="" />