So, reviving this post as I have some photos to share. Well, i've had the photos for a long time and the actual rapid prototype for even longer.
This is a high quality rapid prototype with the thread modelled in and printed. It is designed specifically and solely for the Safari. The Al-Star grip section fits a little differently and also the caps. My idea was to make it for the Safari.
So. A quick summary.
A slave safari is used, the barrel is simply switched out to this short barrel, and a Short Parker Quink cartridge used. The inside of my designed barrel actually compresses the cartridge into the LAMY grip, keeping it tight, secure and impossible to leak. In practice, it writes okay, but the weight and size of the cap makes it feel different to an unposted Safari. It might be possible to improve the feel by shortening the barrel a touch.
I'm not planning to take this to production as I don't see a massive market or any real profit from it. Just good fun and a nice LAMY pocket pen.
Interested to hear thoughts, though.