The third series appeared in 1953 with a larger 2,451 cc version of the engine. The rear of the car lost the tailfins of the earlier series, but was well resolved in a definitive look for the Aurelia coupe.
The fourth series introduced the new de Dion tube rear suspension. The engine was changed from white metal bearings to shell bearings. An open car, the B24 Spider was introduced at this time (1954 to 1955) and was well received. It was similar to the B20 coupé mechanically, with an 8 inch (203 mm) shorter wheelbase than the coupé. The fourth series cars were the first Aurelias to be available in left-hand drive; fourth series Aurelias were the first ones to be imported to the US in any number.
This model was immortalized by Dino Risi's 1962 movie Il Sorpasso (The Easy Life), starring Vittorio Gassman. The actual car used for shooting (a single model) was not destroyed during the accident scene sealing the end of the story: an Alfa Gulia Spider was used as replacement.
The fifth series coupé, appearing in 1956, was more luxury-oriented. It had a different transaxle (split case), which was more robust and similar to that used in the later Flaminias. The driveshaft was also revised to reduce vibration. Alongside the fifth series coupés was a revised open car, the B24 convertible. This differed from the earlier B24 Spider, having roll-up windows, better seating position, and a windscreen with vent windows. In mechanical aspects, the B24 convertible was similar to the coupe of the same series.
Power was down to 112 hp (84 kW) for the 1957 sixth series, with increased torque to offset the greater weight of the later car. The sixth series coupés had vent windows, and typically a chrome strip down the hood. They were the most touring oriented of the B20's. The sixth series B24 convertible was very similar to the fifth series, with some minor differences in trim.Source: Wikipedia.