It's the Stage II cylinder heads that were way ahead of their time. Manufacturers of aftermarket cylinder heads for other engines (V8) continue to come out with heads that in one way or another use some of the advanced design features of those marvelous cylinder heads.
The thing is, they really shine at ultra high rpms. Closer to 10,000 rpm on a big cube motor.
It is the awesome Stage II heads that put Buick in the history books.