I'm curious as to what is the earliest known uses of the 4R/5R cases in the 911? I know they were used in many of the '72 and '73 cars, but I also have heard there are instances of the 7R case being used as early a '72 (or earlier?). Were the 4R/5R cases used in '71 or '70? Does anyone have a good answer?

Thanks

Brooke