It's not all plain sailing, as we will now discover. First, I took out the post-1938 front frames (Part P16 and P17) from the etch:
These have two layers, with the riveted layer being attached last of all.
The inner layer has no tabs at all along the base, so trying to hold it in place is going to be the very devil:
Note that the left-hand frame has a tiny notch in the top - this is where the lubricator and its bracket will be places.
Now, let's have a look at the underside, so yis can see what I mean: if the slots in the footplate are going to be that long, why not have tabs on the base of the front frames to fit into these, and provide a stable location?
"Weshty": what d'ye think? Is it worth modifying the etch artwork?