Hi Alex,
your wish is my command; just a quick shot:
Just a quick picture; this one passed the trials of the Neuchatel Observatory in 1961.
It seems there are only two units by GP and these may be "test" devices; back then, GP was doing extensive research in the field of highly accurate timepieces, which later resulted in the "ChronometerHF" and "Observatory Chronometer" models incorporating the then new fast-beat escapement technology.
This of course is a slow-beat variant with a very large Guillaume balance; as you may see, the anchor bridge comes with a steel plate setting for the jewel, which i haven´t seen in any other Peseux 260 so far. The fine regulation is different from others (you may notice the hairspring studs and attachment, which is finely adjustable).
The P260 is a rare breed indeed and there´s quite some mystery on these, as well as the brands to use them.
So we´ll have a closer look at some later point, when the history of this one may be unravelled!
Cheers,
Peter