Two of my Clauds - a 67 Super Coureur and a 1969 Electron Super Five - have that particular type of Williams chainset, so don't rule out CB yet! My 1963 Super Coureur does have the triangular design on the top of the fork crown too.
Early in the sixties, Clauds did come with steel stems -
(Catalogue image cheekily borrowed from http://www.nkilgariff.com/
If it's an "Il Primo" stem, I think thee should be a small circular Italian flag coloured enamel badge on the top f the stem...
After Holdsworthy bought the trademarks, weren't CB, Grubb and Macleans frames frequently the same as Holdsworth models?