Thanks Robin.
Were there fakes around? The so called Walther Sport I saw was clearly marked with the Walther name. There was only one thumbwheel. A bolt on the LH side passed through the LH sight side and screwed into the thumbwheel; this was into a threaded 'tube' that was part of the thumbwheel and passed from the RH side of the sight across the dovetails. On fitting to the LGR, this threaded tube clearly just contacted the top of the LGR cylinder so that when the thumbwheel was turned the 'tube' in contact with the LGR cylinder moved the sight along the rails.
The mysteries deepen.
Cheers, Phil