you will need Bachmann wheels and Nem coupling other may work
There were built for the ROD Royal Ordnance Division during the First World War
for Armstrong Vickers 12 inch railway gun
Elswick Ordnance Company 12 and 14 inch railgun such as Oxford Rail model
there are photos of at least one wagon in LNER during World War Two.
You are buying an non assembled plywood and card model kit
Kit requires assembly and painting, some parts may need filling
see photos,
glue and paint may be required
I use Bachmann 36-028 Metal Split Spoked Wagon Wheels 12.6mm.
Hornby x9289 Nem couplings.
bogies and buffers are 3d printed some filling may be required
If not in stock allow one week to manufacture
Royal MailSigned For 2nd Class
Made with 2 mm MDF and card
video of wagon running on my layout