Come on the Google experts - RD400F Caliper diagram

[Gingernutz]

I'm a bit stuck with the XS400 - it turns out it has an unusual front caliper normally found on an RD400F Daytona - I have two manuals and neither tells you how to take it apart because they describe another type. I've googled until I'm frsutrated but can't find a manual
This is the one on my bike


Looking at this view the flat head screw in the haynes manual is nowhere to be seen


Any ideas?