Interior door top question (early 911)

[techweenie]

Okay, I have a set of door top bolsters that are steel with a thin coating of rigid material and glued-on vinyl wrapping.

They are rounded like later cars, not squared off like SWB pieces I've seen. I've had mostly '72/73 cars, so I'm used to the plastic formed pieces with steel reinforcement.

Can anyone say definitively what years of cars had the rounded steel bolsters?

(photo to clarify which part I'm speaking of, though the actual one pictured is a '72/3 style)