I haven’t built one of those but they look a bit like the JLTRT ones I made. With that proviso, what I did was:
Bend strip bit so tags go through slots in the plates with slots in. Solder, clean excess tags off back. Drill a couple of holes through the backplates, solder a couple of 10BA screws to the backplate, drill matching holes in coach end so you can put nuts inside the coach to hold it on. Paint. Glue the concertina into the backplate assy.
I guess you would solder the hanger brackets to the end of the coach, probably drill the short flat for the hanger wires first. I think the long flat is the lower end and appears to have a spigot that will need a hole in the coach end.
I’m guessing now, the short L brackets should be soldered to the inside of the rubbing plate, I guess where the half etch lines are. probably drill them too.
Paint the rubbing plate & glue to end of concertina. Stick wires through holes. Maybe evo stik rather than solder for flexibility.
Does this help?
Best
Simon