While I was fairly happy with my soldering of the chassis I do think hiding most of it behind a layer of paint improves things no end! This is by no means the final layer of paint the chassis will see, but I decided to get a base coat on (it's Humbrol matt black primer) and to paint in the flycranks before going any further. The next step is to permanently affix the coupling rods at which point it would be difficult to paint the chassis, and almost impossible to neatly paint the flycranks.
There are still a few parts that need to be glued or soldered to the chassis, which I can't fit yet, so I will have to remove small areas of paint to get a good joint, but it should be easy to touch up the paintwork, and anyway most of the chassis is hidden or will be shadowed by the body.
The good news is that having stripped it down, painted it, and then reassembled it, it still runs nice and smoothly.