XXL Lego

Does anyone know anything about oversized LEGO display bricks? I recently bought seven LEGO bricks at a flea market. They measure 50 × 25 × 18 cm and weigh about 1.1–1.3 kg each. They are hollow, permanently sealed (not storage boxes), and have “LEGO” embossed on every stud. There are no visible part numbers or manufacturer markings. The only thing I’ve found out is that these specific LEGO bricks may have been used in LEGO Stores for displays or retail merchandising. Any information would be...