I had the same problem since forever. When i adjusted the clutch as you shown was just be able to operate the pto. On second look i've found outthat there are 3 bolts as well on the clutch levers where the pressure bearing pushes and they where uneven. So i had to make a couple of tools to reach inside and i adjusted them as well. Now the thing works fantastic and engages without grinding. Thank you for that!
I found this for a MF135 that has many of the same things :-) But it sounds like you need a manual for the engine instead? vieux.tracteurs.free.fr/pdf/MasseyFerguson135_manueloperateur_1974.pdf