I still value your helpful comment though. I am going to rework the loco this evening.
The couplings are to found on all preserved steam locos - the simple chain was known as loose-coupling as persisted for far too long - until British Rail banned all remaining private owner wagons. The speed limit with these simple couplings was never more than 15 miles per hour!
The only real development was to replace the 3-link chain with a ‘screw-coupling’ arrangement which alowed higher speeds - known as close-coupling.
Things have moved on a bit now…
O yes - and a man had to stand on the track between the buffers to couple the train - many awfull accidents were inevitable.