Progress at last (for me): I have stuck on the top of each of the Hornby sides a strip of 40 thou (1mm) black plasticard to imitate the slotted strip that is on the top of the Hachette SK sides into which the roof clips.  And indeed it does and the coach holds itself together, like the original -amazing!  Needs a little bit of trimming to make sure everything lines up and sits tight.  Now I need to cut holes in the Hornby interior to give clearance to the bogie pivots and the close coupler cams before screwing that down.  Then its filling, painting, lining, glazing .....

A 4mm wide strip of 40 though black plasticard with slots cut to match the Hachette roof, (note not symmetrical and handed).  This was welded to the top of the Hornby sides

This cruel blow up shows one attached to the compartment side in place.  I stuck a strip (10 thou) on top of the Hornby side as it seemed fractionally too low

This shows the roof 'pugged in' to the side and proves the concept works ( for me at least this time!)

The assembled coach, externally not too different to the head picture of the previous blog entry on the build, but now it is all clipped together and holds just ...

This is the corridor side of the clipped together coach.  Much work left to do.  The hollowed out under frame is just visible ...