This part applies to manufacturers of passenger cars and trucks, buses, and multipurpose passenger vehicles with a GVWR of 3,855 kg (8500 lb) or less and an unloaded vehicle weight of 2,495 kg (5500 lb) or less. However, this part does not apply to any manufacturers whose production consists exclusively of walk-in vans, vehicles designed to be sold exclusively to the U.S. Postal Service, vehicles manufactured in two or more stages, and vehicles that are altered after previously having been certified in accordance with part 567 of this chapter. In addition, this part does not apply to manufacturers whose worldwide production of motor vehicles is less than 5000 vehicles in a production year.