Try bleeding the 2 ports on the master cly first.
Then, follow the lines from the master cly, go to which ever line is the farthest away from the master cly (should be 1 of the rears) and start bleeding air until you get good fluid coming out. Then go to the other side and repeat process.
Repeat the same process for the fronts (starting with the line farthest from master cly).
Once you get good fluid at all 4, I go around again and do a "good bleed".
If this does not give you a good firm pedal, somethings sucking air.
Pull the rear drums and see if the rear wheel clys are wet (around the seals) if they are ok, master cly.