A Tale of Three Calipers, Tell me about different RIBE hardware Options

[zoomCat]

I'm putting together a pair of rear calipers for a six, which the previous owner had replaced with 911 rears to get the vented disks. He didn't keep the originals, it was back in the 80's and nobody cared.
Here's what I've got so far:



On the left is a rebuilt stock 914/6 left rear. The plan is to add a spacer for vented disks.
In the middle is a 914/6 right rear, which I got years ago that already has a spacer. It will be rebuilt.
On the right is what I think is a right rear Ferrari 308 caliper, because the bleeder is in the wrong place. It can be a donor if absolutely needed. The rears the previous owner had installed are the first candidate for donors.

My question today is about the RIBE hardware.



On the left is the rebuilt stock, on the right is /6 caliper that had a spacer added. The fasteners on the left have sloped shoulders, while the other has more square shoulders, which I see on the front A and M calipers I've got.

What was original, either for the stock calipers or the GT calipers?
Is there any functional difference? Esthetically I'd like to get it all matching and correct before I send it all off to PMB, but that depends on availability.