1st regarding lighting. There is no way I either want, or intend adding lighting to those 4 wheel coaches.
Firstly they were most likely using oil lights, although gas would have been an option by 1930 which was
the last date on which a scheduled passenger train went into West Bay. Such lighting would be rather dull
and only show when operating in a darkened room which will not happen.
Now Dave,
Those modern skinny couplings are Bachmann, they do two lengths and short is usually best for most wagons.
They both (lengths) come in packs of 10 with NEM pockets. I try to have all my regularly used stock fitted with
them.
The key components are the Peco PA34 mounting blocks. These come in packets of 10, where you get 5 sprues
with two on each, that being enough for a single wagon. The complete packet therefore has enough for 5 wagons.
Last time I bought any I thing they were £3 a packet. DO NOT be put off by the description saying for cranked
couplings, but what you have to do is slightly modify for each application, These mounting blocks come with an
extended rib at each side, sometimes these are removed to leave a flat base, here is a Bachmann long coupling
and NEM pocket pressed into the mounting dovetail.

One of the easiest fittings is to Dapol Wagon Kits where the original round mountings moulded into the floors
is at the correct height for the PA34's when those two ribs are cut off. I also lightly abraid the flattened surface
to assist a good liquidpoly attachment.
Here one is stuck in place and you can just see the round stub onto which you attach them. Very occasionally you
need to just trim at the back to make certain you don't foul the axle. To get a slightly reduce gap best to stick so
the end of the NEM pocket sits halfway into the bufferbeam thickness.

Here you can see one still on it's sprue, one with the full ribs, and two where the rib have been trimmed away and
the flat base roughed up.

On other kits you need to build small platforms and sometimes the full rib remains, other times one trims a small
sliver away. Always to get to the height of your 'best' Bachmann wagon before adding the liquid poly. I alway match
to another wagon as you can adjust about 1 mm up, or down while the glue is still very wet. I like to match to as near
to exact as I can.
An example of checking that a Cambrian Mermaid coupling is at the correct height.
The couplings must be on the wagons centre line, square to direction of travel, with no sideways twist. Getting that final
'set' right is always a few panic moments 'cos the glue's drying with every passing second !!

Is that clear enough ?
Geoff T.