I started researching the details that are left to add and continued fabricating small fiddly things like brakes then the realisation: before I get much further with the detail I should ensure that it will actually work. 

Something that I should have done before soldering anything to it was gap the PCB footplate on the bottom to maintain the isolation of the split frame chassis. This was completed without destroying anything much of what was already attached. The valances came away in two places where the tack soldering gave way.

I removed some further material from the side of the firebox such that the worm mesh can be checked and the packing adjusted until it looked right. There is just a little further material to be removed from the packing at this stage.

The hole is well hidden from view once the top is on. You'd have to be close up at track level, and looking upward, to see it. 

Soon some testing must take place and that could mean playing trains. Buffers and couplings will be needed for maximum enjoyment. With the help of Steve and Nigel I found some buffers in the 2mm range that have the partial taper of the 'Churchward' type. They're not perfect - no step and the mounting plate is circular, not square. Looking at the above photo I can see the footplate is no longer a straight line and the join where I put the valance back behind the front step is quite obvious. Cruel are these photos at multiple times full size. Something that had been bugging me was the reversing rod. It was previously too high, slightly above the splasher. Photos suggest that it goes behind or the splasher is relieved to allow it to fit so I removed and reattached it lower down. I think it might be a little short now. Maybe the engine is in reverse gear?

As previously estimated only a small amount of packing was required - less than 0.010" - fixed and filed down. Easier this way than trying to lower the motor. Had much more packing been necessary for mesh additional material removal would have been required from the tank/boiler casting (what's left of the Farish body on this). 

With some superglue fixing the worm in place and a few volts applied to the motor wires I have observed the wheels turn once again. This was somewhat brief: After several full rotations the superglue bond gave up. Perhaps some further investigation required to see if this is a real problem or just poor gluing.