Seamus,if you are referring to the NIR open wagons that were cut down,they were cut down as they were used as a basic ballast wagon where a gang of men just shovelled ballast over the side! I witnessed this operation in the early 70s on many occasions,with one of your favourite wee loco's,the DH in charge. I have cut down a few of these wagons for my layout,will stick a pic up of the operation for you soon.
JHB-superb pictures and great info to go with them,get that lot into a book,it would be worth it.