According to noted N scale historian Charlie Vlk, these are built-up versions of old Dimi-Trains kits (said kits now being owned by Tichy). The "Wood Chip" and "Sugar Beet" gondolas look (at least to me) to be the same model. The "General Service" gondola looks to be the same as the "Beet / Chip" models, just without the side extensions. It is also essentially the same as the gondola that Atlas / Roco tooled in 1967 (later copied by Bachmann). One prototype for the car is Rock Island.
These models are different from the Intermountain "USRA Composite Gondola" insofar as the USRA has a blank center panel and the diagonal bracing is different. The USRA also doesn't have the door operating rods along the bottom of the sides.