Yet another clutch adjustment question

On mine, the length is also 2 inches.

The spreaders at the pedalbox are known to wear, the holes become oval which reduces the stroke at the level of the master cylinder and therefore causes an insufficient stroke of the slave.

But I don't understand your third photo

Mine at the moment for what it's worth, works well for me.  I can tell you from my re-install of the return spring, it is on the "perfect" spline for me.  But  it would appear to me that you may be correct in the possibly extra length to your stop.  This is -2.  ZF -1 brackets have some differences.

The measurements are not very precise, but in my opinion
that's not where you have to look for the reason of the malfunction.

It is interesting to look here and on line and see how different so many throw out bearing arms and slave cylinder mounts there are. Certainly things weren't perfectly standardized and probably modified by owners over the years. Geometry says the more vertical that the arm is, the less slave cylinder movement is needed to move the throw out bearing a given amount.

I agree that there may be a combination of factors needed to make this all work properly but for now I am checking off the list doing the easy things first... On we go...

Thanks to all for your help!

I cut off the " free play stop" arm from the top of the splined throw out bearing arm attached to the throw out bearing shaft so the stop would no longer interfere with the "free play stop"  on the slave cylinder mounting bracket. This allowed me to rotate the throw out bearing arm one spline so the arm sets more vertical in its resting position. As expected. the clutch does properly disengage now.  The arm was so nicely powder coated too!!! So I will reweld the free play stop in a different position on the arm much like in several  pictures that I have seen....

Nothing is easy!