You bleed it by removing the little screw between the brake line and the return spring. There’s one on each side of the rear caliper. For the front caliper you’re on your own until I get a better pic but it might be that big screw right on top.
Then you need a way to force or gravity feed brake fluid into the master cylinders. An old mustard bottle full of DOT3 works.
The linkage to the master cylinder is a bias adjuster, it’s going to be different from one side to the other and it will flop all over the place with all that air in the system.
Please make sure the bolts holding the calipers to the frame are high tensile strength and not stove bolts and why is there an elbow coming off the rear master cylinder and not a straight fitting?
Brakes look like early righetti ridolfi?
FAA certified jet engine and aircraft technician,
Nicholson Speedway class champion 2001,
Yamaha KT100 Service Center,
41 years karting experience