take off all the springs and rods and check that the Z bar itself moves without any binding.
Check the rod that goes thru the firewall is not binding up on the hole in the firewall. Or is the pedal itself binding up on the hanger. You really shouldn't need a ton of spring force to bring the pedal back up. Also remember you can change the leverage by where the rods are mounted on the arm on the Z bar. A longer arm gives more leverage but needs more travel.
You could modify the stop for the clutch pedal to come up a bit more. Maybe the brake pedal is sitting higher than it should so the clutch pedal looks lower.