A while ago there was some discussion of poultry stock cars on these pages.
Be advised;
MR published a plan for such a car in their July 1961 issue on page 26
MR published a photo of a model of such a car in their May 1973, page 41.
RMC published a construction article in their May 1951 issue, starting on page 10.
RMC published an ad for such a car from Overland Models on page 43 of their Mar 1984 issue.
Have fun