OK, I had another look at the car today. The brake pedal still went down to the floor but could be pumped up as I mentioned before. With the handbrake off the cables are slack and I have to pull it up 4 or 5 clicks on the ratchet before the wheels are locked.
This is one of the front brakes after I replaced the parts.
I guess these are 7" drums which are correct for my 948cc model.
Today I adjusted the master cylinder push rod, you have to be careful with this and study the instruction book. But so far it seems to have taken up the slack and the pedal no longer goes to the floor... we'll see how it behaves in the morning when all the pressure will have released.
Locknut shows the original position for reference; I subsequently took it up towards the locknut again a few flats. We shall see how the brakes behave now.