removal of broken clip from Swan cap.

[PaulS]

This was how I bought the pen some year or so back, and in my ignorance assumed the remains of the clip would be easy to remove, even if finding a correct replacement might take a while. But the best laid plans of mice and men etc. ........
The pen is a good example of a Swan model 3320, one of those with metal threads on the section - no idea of date of manufacture - but possibly late 1940s - colour is a deep dark blue - nice pen with a broad nib that has some flex.
The Pen Manual suggest when broken as this one is, the remnants have to be removed from the inside. This means removing the inner cap, but before I butcher the cap entirely, does anyone please have any tips to help. thanks.