It isn't hard to find copies of the Series III workshop manual on the web.
The hosting sites seem to be in Russia. Now, how might the Russians end up with workshop manuals for ancient Land Rovers?
Well, considering how many were being used by the military, I'd imagine the KGB amd GRU were buying copies, and shipping them off to their respective headquarters.
So do we have the Russian spies of the Sixties to thank?