So I eventually bit the bullet...
...and gave it a go - here's the result of a misspent lunch hour.
https://lh4.googleusercontent.com/-L...427_125437.jpg
https://lh6.googleusercontent.com/-w...427_125536.jpg
https://lh6.googleusercontent.com/-F...427_133744.jpg
https://lh4.googleusercontent.com/-C...427_133918.jpg
I'm not sure whether I'm happy with it or not to be honest.
I like the Delrin, both in terms of ease of machining and feel in the hand, although overall it's a little heavy. I also like the slightly translucent look.
Certainly glad I did give it a go though, and I'm happy that I've learnt plenty for the next attempt.
Also the engineering metal lathe is not really suited to creating anything other than very exact straight lines, so creating attractive curves is going to take some practice I think!
If I can find o-rings that are the correct size then I'll put one each in the two grooves, although I'll probably have to make them slightly deeper than 0.4mm, as I think the Black / White contrast will help the overall appearance.