Large Cattle Wagon (MEX)
Use the Association BR Cattle Wagon kit (plastic), with the 11'6" DC chassis etch (which provides replacement top doors), lower and flatten the roof, and replace the diagonal end straps with flat X-strapping.
Alternatively a 3-D printed body is available from Ian Smith.
Prototype
Built 1902-1911, totalling about 575.
Fitted with Wright-Marillier adjustable partitions (thus allowing it to be used as Medium and Small as well as Large), and generally vacuum-fitted, either from new or converted shortly afterwards.