Hopefully someone with more knowledge of styles and policy will be able to help you.
Personally, I find clans to be a bit of a difficult concept. Those of us who were born in Scotland tend to look upon tartans and clans as being strictly for the tourists. I was surprised to discover that most Guthries who have taken DNA tests do not actually appear to be related to the Guthries of Guthrie and Guthries of Craigie. In fact, over a dozen genetically unique Guthrie Family Groups (GFGs) have been identified, each originating from a single male ancestor.
According to Wikipaedia:
It is a common misconception that every person who bears a clan's name is a lineal descendant of the chiefs. Many clansmen although not related to the chief took the chief's surname as their own to either show solidarity, or to obtain basic protection or for much needed sustenance. Most of the followers of the clan were tenants, who supplied labour to the clan leaders. Contrary to popular belief, the ordinary clansmen rarely had any blood tie of kinship with the clan chiefs, but they took the chief's surname as their own when surnames came into common use in the sixteenth and seventeenth centuries. Thus by the eighteenth century the myth had arisen that the whole clan was descended from one ancestor, with the Scottish Gaelic of "clan" meaning "children" or "offspring".