Well, the plot thickens, kind of.

I've downloaded an Escort Haynes manual and found out a little bit more.



This little diagram suggests that the valves in the pic of the
Escort donor's brake master setup up are indeed pressure valves,
presumably to stop the rear brakes locking up when used in anger.

I also disovered that the donor is clearly non-ABS. If it was, there'd be
bundy pipes going back to the reservoir.

The snag is, my picture doesn't clearly show which of the four pipes
on the master go to the back. I've searched for a schematic even
this is apparently in the rocking horse teeth category, or something!

These things are sent to try us...