Hi All,
The end result is a success though the road had some turns and bumps along the way.
First of all Bock does not sell their nibs directly to consumers so you need to order it from a reseller. Second of all you can buy the nib only with the feed and housing.
I’ve ordered my #6 Bock Ti <F> nib from Beaufort Ink from the UK 
for £56.29 (incl. VAT) + shipping. Thanks to the good people at PostNL my package was accidentally sent back without delivery at the exact time when Beaufort Ink was busy moving their shop to a totally different location so my nib got to see the English Channel and the countryside twice 
All this happened before :Brexit: (why is there no BREXIT emoji yet? 
) so be careful with UK orders as the start of the Transition Period is imminent. Who knows how that will affect international shipping?
The Bock feed+housing does not fit the Opus 88 (no surprise here). However the Bock nib almost fits the Jowo feed+housing. The Bock nib is a bit more convex which means that there is a gap between the Jowo feed and the Bock nib. This gap is wide enough to seriously affect the capillary effect so that the tip and the tines of the Bock nib does not get ink. Not only it skips & hard starts, it basically does not write at all.
I asked Anabelle Hiller to use her nibmagic powers and make it work. Though I was present, I’m not sure what she exactly did. Nevertheless she had to use some hot water (around 40°C afair) to be able to gently bend the nib and the feed together.
All’s well that ends well. Now the Bock Ti nib works great with the Jowo feed in the Opus 88 Demonstrator. No skips, no hard starts, no railroading. I’m very happy with the result and it proves that a #6 Bock Ti nib can be fitted into the Opus 88 Demonstrator.
Disclaimer: Titanium nibs are rather soft and pseudo-flex than springy and truly flexible. It’s easier to spring a Ti nib than a steel or gold nib. Be careful when flexing a Ti nib.