So here is the finished product - and black certainly suits this model well. The steering wheel is in place and the wipers still work. I did have doubts about the switch as I could not see how it worked to disable to cogs from meshing. There is a metal cam on the switch spindle but it doesn't appear to do a great deal until the base is re-affixed. Then it works so I shall not bother about that too much!
Rather than attempt to paint the headlamps and small horizontal lines at the front, I simply scraped off the paint but I haven't yet completed that task and need to removed a bit more yet and then polish the mazak to make it brighter. The small horizontal bits of 'chrome' will be fine, however. I am also trying to think of what I might have that could be used as the missing emblem.
All in all I am pleased with this. The original model would probably not have found a buyer in years and even then only at £20 or so if I was lucky. This is definitely worth that to keep.
The Mercedes-Benz might have sat well next to the recently rebuilt Bentley but there is a scale problem. They'll need to stay apart, but maybe not the regulation 2 metres!