If I’m reading it correctly, you have adjusted the handbrake cable length, on your brake drum set up, in the hope of increasing the handbrake efficiency-?
If that is right, you have gone about it incorrectly.
You now need to safely Jack the car up and disconnect the handbrake cables from both back wheels. Having done that, you now adjust the brake shoes to the normal degree. When you have done that, you reconnect the cables ( probably having to lengthen them) and finally adjust them until you have acceptable braking at 4 notches.
If it were mine, I would be removing the drums and cleaning and inspecting linings and wheel cylinders, and obviously replacing any faulty components.
