My revised idea for how to cast the bogie extension for the MoD Flat Wagons seems to work.
I've had to beef up the frames at the sides but that's probably no bad thing.
And in putting together this first one I followed my hunch that you'd get a better result if you glued on the side pieces before cleaning the flash from the main frame part.
The very thin film is effective in disguising the joint and, I hope, makes it easier to assemble what are quite small parts.
The last part of the bogie to design is the very chunky brake levers, but I might leave those to one side for the moment and concentrate on the body of the wagon instead.