Windows, doors, wheels, steering : everything can be moved with 17 ERCDials ( what a difficult work!). The PD-4501, the most distinctive American parlor bus design of the modern era, was the result of five years of GM Truck and Coach Division effort based on a design by Raymond Loewy as U.S. Patent 2,563,917. The design is listed under the U.S. Patent D175,464 with Roland E. Gegoux as its designer. Originally conceived as a 35-foot (10.67 m) bus, Greyhound used a tandem-axle, 40-foot (12.19 m) prototype called the GX-2 to lobby for the lifting of restrictions against operation of 40-foot (12.19 m) buses. Power was originally provided by two GM Diesel 4-71 engines driving through a fluid coupling because the 8V-71 engine was not ready for production. This installation proved to be less than successful, and the 979 buses remaining in 1961-62 were rebuilt with 8V-71 engines and 4-speed manual Spicer transmissions by the Marmon-Herrington Corporation. The original design prototype for the Scenicruiser was a double decker with access from the first level. The driver would look to the road from the second level. It was soon decided that it would be a split-level instead, with a lower level containing the driving console and 10 seats behind it, and the upper level containing 33 seats. This arrangement also allowed a baggage compartment underneath the second level, while providing 360-degree view for the upper level. A lavatory was located on the rear of the first level. The Scenicruiser was equipped with air-ride suspension and air-conditioning.