Thanks Hedd, I think the much earlier CAV headlamps were more bell shaped. As you say Lucas acquired CAV and Rotax in 1926.
I am interested in point your about different sizes. I had naively assumed that there was a limited range of stirrup sizes, say 8,9 and 12 inch that were commonly agreed upon (a sort of industry standard). I had not considered they may vary between manufacturer. Since I don't have the stirrups it is academic - when you find me some, I will make brackets to suit. 🙂
Dave (S&F)