Yes, 1965 is correct. Here's your next point.
From 1963 to 1965, bus production at Fritz Fleischer KG came to a virtual standstill due to the large order for the production of X-ray trains.
However, repairs were still possible and designs for the next generation of buses, the S 2 RU, were already being finalised.
In this context, there seems to have been time to design the frame of the Müller bus. The frame was then built at Müller on a chassis from Gräf & Stift. They would have liked to place the engine in the rear, but this was not authorised by the licensing authority. The motorised frame was then driven to Fleischer for planking. Pure adventure!
I am attaching photos of two other vehicles from the Müller fleet.
Immediately after the Second World War, a wooden gas lorry was provisionally fitted with benches and a roof. The excursion bus was ready.
From 1969, further buses were built in co-operation with Fleischer. Here is an example.