Jonathan,
Thank you very much for pointing me to AMF87, the Euro price is eye watering for me! But a few intriguing wagons popped up. I am taking liberty to post the images of the wagons from the AMF87 website and translated extracts from the website as well.
First is a WD well wagon (AMF kits K220 and K221) which was produced in a short and long version: the translation from AMF87 states: "These lowered cars were built for the British War Department during the First World War, arrived in France in 1918, several specimens were embedded in Park Co. North with 2 styles here reproduced 13.2 m and 17.7 m (which make a very long car for the time), some of these cars were modified wagon obviously central. All had a very long career and experienced for most registration UIC." Comment: I suspect these wagons would have been introduced for carriage of the Mk IV and Mk IV tadpole tanks, the tadpole being noticeably longer than the MkIV.
The next is a 20 tonne metal van (AMF kit K240), the site states: "These cars were built in Britain at the end of the First World War on a model derived from boxcars to 20t skins friezes wood Co. North and attributed to it in compensation for losses suffered during the conflict. The body is full metal, a characteristic they share a little later with the North covered unified "rebuilt" with domed roof."
Third is a WD Guard Van (Kit K241) : "These cars were built in Britain at the end of the First World War for the operations of the British Army in France. After the war they were sold to the Compagnie du Nord. They share many common elements with the boxcars built simultaneously for the same reasons. Originally vans were equipped with a corrugated tin roof and a large periscope, some were also equipped with a hand brake screw gangway to make them linkable to increase the weight of the trains brake while n 'using the services of a single agent. Quickly, roofs were redone in a conventional manner (wooden slats covered with tarred canvas), lost their gangways for those who had received him and provided a smaller periscope."
Finally there is another short wheel based van mentioned with commentary mentioning WD relating to the Brake Van, but the translation is not quite clear, overall very interesting, a pity they are not in OO. Given the cost for these HO kits and the likelihood that they will be noticeably smaller with OO stock something I am unfortunately not willing to risk buying.
With regard to the SNCF Society, no I haven't, though given my quite narrow and specific interest I am not sure joining would be worthwhile.
Cheers,
Chris