Dieseltech has summed up most of the procedure, however no mention has been made of the removal of the three slave screws from the clutch cover. Have you removed these. It may sound like a dumb question but it has to be asked.
Assuming that you have removed the screws, what figure have you set the adjusters to? The target figure is 090" but 080" should be OK. It is more important to have them all the same.
Using a flashlight through the underside access hole have an assistant press the pedal while you watch the operation on each adjuster. When the screw heads strike the PTO pressure plate they should push it rearwards by approximately 1/16" or 1 1/2 to 2 mm. Ensure that you have approximately 3/8" clearance in the free travel at the point where the pedal contacts the footbar.
If your adjustments are correct the PTO should stop turning when the clutch pedal is approximately one inch from full travel downwards. This margin should always be present for safety. As Dieseltech has mentioned if the PTO starts again then the release levers will be in contact with the rivet heads on the PTO plate hub and must be readjusted. If this occors it can normally be heard.
DavidP, South Wales