I'm looking around to see if I can find a service manual to look for clues.
The only thing I can think of off the top of my head is that maybe the push rod is keeping the arm from fully seating in the case. Have you tried to remove the pressure plate and push rod, install the clutch release arm and then reinstall the rod & pressure plate? the rod may be what holds the clutch arm in place.
Look at the clutch arm. the end that goes in the case with the flat, does it look as if the push rod will keep the arm from sliding out if you install the release arm in the case first and then insert the rod and pressure plate?.
If I'm looking at it correctly, your saying the release arm is sticking outside the case about the same thickness of the pushrod.
I'm just throwing this out there, I'll keep looking for a manual..
Tuck\o/