Anon,
The photo was published in one of the issues of The Eagle – the magazine of the Glider Pilot Regiment Association. I know I’ve got it on the bookshelf somewhere but give me a couple of days I’ll find it. Theres about a thousand bookmarks stuck to the pages to wade through.
Theres quite a few Horsa’s in UK museums althought mostly their of the Mk.II variety as those were still in service into the 1950s. Generally speaking if you inspect them in details they tend to be late service models based on the modifications on them. There are few Mk.I fuselage sections as those were popular for various uses post-war so tended to survive.
To the best of my knowledge and research, the Army Flying Musuem at Middle Wallop has the only existing original Mk.I cockpit in existence. It’s an interesting example as it was built by Elliots of Newbury and seems to have never been fully completed so acts as a hugely informative and useful reference to how the gliders were constructed.
If you want to see a very early (1943) spec Mk.I cockpit being built, we’re in the process of scratch bulding one at the Jet Age Museum, Gloucester.