Well Dominique. it wasn't too tough.
I took a piece of 5" cold rolled C1020 mild steel. Bored it out to a suitably thin wall and then deep enough to fit all the chronometric works. I didn't make any drawings so nothing really to send you except a picture.
I initially made it to fit a chrono set I had that used the external gear drive on the back but the case was far too deep, so I swapped those internals for one that used the integral gear drive on the back which is much shorter overall. I got a new bezel from I think KTT in Australia back then (mid 1990's) and turned up the threads to suit. Local glass shop cut me a glass and i made some gaskets.
The cable drive just exits a hole out the bottom and all the internals or held with three screws through the back of the case. I made a suitable mount but had to re do that as the weight of the whole thing was too much for my first rather delicate mount and it broke on a trip to California.
Andy Rackstraw in NZ made the faceplate. He did three of them, (It only took a few years, I had even forgotten about asking for them when they arrived in the mail!). I have one, I gave one to Dan Smith and it is on a typical cast 5" speedo on his daughter's Rapide and I think I gave the third to Somer Hooker....
I have seen JRO 102 but didn't take any photos so have no idea how close to original it is. People seem to be far more clever these days and get far closer to original. As my cases are much earlier and I can run any silly UK style reg plate it has JRO 101 on it.
If I was to make another - which I am not - I would just use a nice 5 in OD tube and weld the back into it and machine to suit. Boring out the case took quite a while and made a big mess!
I don't have any close up photos of the speedo but here is one of the bike.