69 Early, just how much "rounder" is the bracket of the ones you mean? I'm just curious to get more details. The one pictured is the Ford type and can either be had from a Ford (obviously) or from CIPA in the aftermarket. The other company that has made that type for years is Delbar and I think they are still available. That's what I have on mine. The brackets are a little rounder, but not much. The mirror heads are just a tad more squared off around the edges, though still rectangular in profile. And the "feet" are a little more universal.
BUT, the brackets ARE close to what you say, I think. They measure about 5 1/2" at the pivots, but the actual arm is taller at 7" from top arm to bottom arm.
Don't know if that's what you're looking for but thought I'd throw it in there.
You might look at the CIPA website (if they have one) to see what they offer.
Paul