Thanks to all those who tried to guess which pen was illustrated. Chris J is the winner. He guessed that the pen was a Conway Stewart 205. Several people were so very near!
The pen is not illustrated in Stephen Hull’s book. I think most people were consulting the late Jonathan Donahaye’s wonderful listings but he only shows an earlier, flat-top version. The one place no-one thought to look is in my blog. A Conway Stewart search of the blog would have taken you right to it! I wrote about this excellent writer some years ago.
Congratulations to Chris J for his detective work!