UPDATE:
I have decided that the above plan, appealing as it was, is totally impractical for the space I have available and my meagre transport capacity.
But it was nice to imagine!
Actually yes.....there are a few small tweaks which could be made:
* Open out the top of the chimney (these are solid on both my OO Works locos)
* Coal in the bunker
* Crew in the cab
* Valve gear underneath (access easier from the fireman's side)
* Subtle weathering
This could become obsessive!