In 1970, all three blocks grew in deck height and gained a new head design. These changes made this the third generation of AMC V8, hence it is sometimes referred to as the "Gen-3" AMC V8. The stroke and deck height on the 290 and 343 were increased by on both engines, becoming the and , respectively. The 1970 AMX 390 remained at the same displacement by using a special rod and piston for this year only. It is believed that AMC kept the 390 this last year due to the reputation it had garnered in the two seater AMX, which was discontinued after 1970. In 1971 the 390 was also stroked by to become the 401 engine.