E-Brake help please

I think were not talking about the same area of the strut.
On the right side of all the 11" brake struts in your first picture, the end with the spring on it...compare that to the same area on the 10" struts in your last pictures. THATS where the obvious difference is in the two pieces.
I know the end is bent over on both 10" and 11". The difference is HOW MUCH of the end is bent over. The 11" piece has a much larger part of the end bent over than the 10".

That is true, but it doesn't matter. It's not like you can exchange 11" and 10" brake struts. I was talking about the offset bends on the ends of struts, none of them are straight. And they all have the same offset.

So, to clear all of this up I went out and pulled a brake strut from a set of BBP 10x2.5" brakes I have on my 1971 Satellite (same as on an E-body). I also pulled one from a SBP 10x1.75" set I have on an A-body 8 3/4. Here's what they look like. There is a slight difference, the offset of the ends is the same, but the thickness of the strut is different (shown with arrows). The SBP 10" brake strut has a flange, and that makes the strut narrower through the middle.
IMG_3417.jpg
As it turns out, this is where I messed up. Not all 10" brake struts interchange. They're forward compatible, but not backward compatible (at least without modification). Meaning, you can use 10" SBP brake struts on 10" BBP brakes, but not the other way around. 10" SBP brakes need 10" SBP brake struts. The offset on the ends of the brake struts is the same, the bends are the same. And either strut clears the backing plates regardless of which backing plate they're on, SBP or BBP. But, the additional thickness of the flat BBP struts causes interference on the back of the axle flange when used on the SBP 10" brakes. It's not much, only an 1/8", but it doesn't work. You could probably clearance them, but, they might not be strong enough, hence the flanged section on the SBP brake struts. What you could do is put the strut in a vise and fold part of it over so it looks like the SBP strut. That would clear, it would be plenty strong, and since the offset is the same it would fit. But, they make re-pops of the SBP struts, so unless you're cheap you don't have to do that.

However, it doesn't matter for 10" BBP brakes, as shown (no, the springs aren't hooked, but as you can see everything is seated properly, it works)
IMG_3415.jpg
IMG_3418.jpg

So, if you're switching from SBP 10x1.75" rear drums to BBP 10x2.5" drums, you CAN use all of the same hardware, it all fits, no problems. What you can't do is use stock, unmodified BBP 10x2.5" brake struts on SBP 10x1.75" brakes, and I was wrong about that. But all of the other stuff works, levers, springs, adjusting hardware, and cables. But not the BBP brake struts on the SBP brakes.

As for the 11" stuff, all of it interchanges. The brake struts from 11x2" brakes work on 11x2.5" brakes, and vice-versa. I tried it, it works, it doesn't matter if the struts are flat or if they have the flange, the offset of the ends is the same and they all have clearance to the axle flange. The "bent" section that captures the shoes is the same length on those as well. In fact, the flat struts are the same "thickness" as the flanged ones. Not sure why they changed, obviously the struts with the flanges are stronger than just the flat ones.