Stylistic Influences

That's because Bill Mitchell was involved with both the '63 Riv. & the '63 Vette.

 

In my book the '63-65 Riviera is one of the most beautiful Buicks. Ditto the '63 among Vettes. But I never completely warmed to the boattails, despite the obvious influence of the Vette rear.

 

Also look at the 1935-36 Auburn Speedster for style cues in the 1971 Riv.