Hi Warren,
It was just a thought after reading the earlier comments. Looking at your superb lining on the Britannia I would agree entirely with what you say.
However, I think the key to success above all is the practice. Good brushes and ruling pens can easily be sourced. In fact I have dozens of pens in my collection in sets and also loose pens bought separately. More or less they all draw beautiful lines with ink and paint, but apart from the odd panel on the valances of my BR Std 7 and Std 8, I use Fox lining transfers. It's not that I think they give a better result than can be achieved by Artists such as yourself, it's just that I don't have the skill to use the pens and brushes and I don't have the time or models to gain the skills. So for me personally, the transfers are the better option.
However, I will try the Kern curved line pen with a small template just to see if it can handle the small radius curves expertly painted by yourself with a brush. I'll do it with ink an paper and if it's any good I'll let you know.
All the best,
Peter