Richie,
I dug out one of my 1980's wagons to get pics of the home-made S&W couplings. I have to apologise for the less than perfect condition of the wagon but it, and another dozen or so wagons, were built from etches that Alan Gibson had just brought. And I was trying to get enough of my own stock to run on my layout at exhibitions and the next exhibition was about a month away.

So it was hell for leather to get them ready and in some sort of fit state. And of course they never got overhauled to sort out the problems.

I had exhibited the layout on a few occasions up till then but it was a layout of Dursley and the locos and rolling stock were loaned from other members - a Collett tank from Bill Sweet, a Pannier from Les Bevis-Smith, a Metro tank from Alan Cruikshank, and a load of GW rolling stock also from L B-S. There was a general feeling that I had to get my finger out and get some LMS locos and stock on it. I was also building Alan Gibson's 3F kit as well.
Here's the hook end :-
...all from brass wire and a three link dropper with an iron link on the end.
At the bar end it's a simple loop of the same wire soldered behind the buffer beam.
Here's what went on underneath. :-
A bit of heavier brass rod was soldered to the brass floor and bent to provide a pivot for the coupler's hook. The hook wire was soldered to a piece of brass tube which fitted on the pivot bar. The bit of blue material is a bit of insulation from a cable used as a retainer which was a nice push fit on the pivot. The hook wire was counterbalanced by the lead fishing weight to the right of the pivot, and this could be finely adjusted by sliding it along the wire until a good balance was achieved, then squeezing the weight with pliers to fix it.
The couplings worked really well and there was a fair amount of latitude in settings. I had a fairly tight radius in one road of a three-way turnout in my yard and I never had any problems with missing the loop if I had to couple on that curve.
I think I would now make the hooks a bit finer and reduce their dimensions by about half and they would still work well. We tend to have pretty good track on S scale layouts so we should not be worried by vertical variations in height of the couplers.. Bill Sweet was giving a fair bit of help in doing the couplings and we played safe with generous dimensions. The couplings on this wagon could cope with a vertical variation of about 3mm.
The buffers were what I could source from 4mm components. I had the good luck to have Max Williams' shop in Bristol close at hand which had an excellent range of 4mm components and I went along his shelves with a rule until I got something close to scale. The buffer heads were intentionally oversize to avoid buffer-locking.
On the other matter in this thread, the archives of the North British Loco Works were discovered at Kilmarnock. When the NBL closed in the 60s, Barclay took over the good will of the NBL and the drawing archive was transferred to Kilmarnock. This was discovered when archivists went down to acquire the Barclay archives when that company closed, and discovered a whole lot more.
Jim.