Hi!
The position of the reservoir is a bit wierd. Judging by the picture the copper pipes seems to be higher than the lowest point of the reservoir.
Make sure that the brake hoses are OK. With the years they convert to turkish delight inside no matter if they look nice from outside. They are totally plugged or play as a non-return valve. If they are old enough, just change them anyway.
One last thing. Check if the pedal rod needs to be released. There must be a clearance of about 0.2-0.5mm between the rod and the master cylinder piston or 3-5mm free stroke on the end of the pedal. Not sure about the numbers, better check with the books. In case that the pedal is compressing the pistons, the inlet ports would be closed, so no chance for the fluid to pass through.
Have a nice evening!
Best regards!
Deyan