The J2's were from a series of hastily produced freight cars which were used as demostrator models to complement Bachmann China QJ's steam locomotives. The first production in year 2000 included a single version in red or black and can be identified by the boxes which had a sticky label in the corner which extends over the perspex window and no road numbers. These are really quite rare as they were only available to dealers, however many were later sold under the table after the QJ's sold out. Essentially they are Bachmann Industries silver series freight cars (which make US prototype models), which was a 'marginal step above the low end of the model market. Despite them being US cars, they initially sold very well due to a total market shortage of true Chinese cars. They are still readily available through most Chinese retailers.
The models' major issue is of course that they are USA models with Chinese lettering that bears no reseblance to a real J2 livestock car. The paint work and lettering are extremely sharp. The tooling for them has been around a long time and the physical details are not really all that impressive with chunky ladders and footsteps and other details that are simply molded onto the main body shell. They have opening doors and a seperately applied roofwalk. True, they are pretty cheap, and deservedly so. They're also still readily available and will still fill a niche for some time as there is no alternative Chinese livestock car available.
They have nice rolling chemically darkened metal wheels with low profiles that should be able to run on code 55 track. They are fairly heavy, but not overly so.
Bachmann EZ mates can be replaced with Kadee #5 (standard), #58 (standard, scale head) or #158 (standard, scale head, whisker).
These are a cost effective way of populating your Chinese layout with livestock cars.