More progress:

The bogies have now been built, as per the solebar they are lacking the flange on the top and bottom edge (suggesting adding it with microstrip after completion)

Still debating if I will replace these with an alternative.

there are two components that appear to be steps, that between a look at the Russel photo of the 7ft American bogie, and looking at the etch I cant work out where it goes.

On the body I have made a start on the underframe trussing, fabricated from L shaped brass section. I started by making 2 vertical razor saw cuts, one at each transition between the centre flat section and the angled sides. The two uprights were cut from the same section, these cut over length, with a 3mm flat filed on one end to over hang the edge of the centre section.

This was then all soldered up before filing back to get a square joint.

The question now is how to fit it. Looking at photos it should attach to the lower flange of the solebar (which is currently missing from the model) My plan is to add the solebar (depending on what I can find, brass or plastic channel will be used), if its brass channel then I will solder into the correct place. If plastic, then it gets more interesting...

Still also need to solder on the last few end steps, before I can start gluing the small details on (hinges etc that I am not happy soldering)

Will post more photos tomorrow hopefully