Hi, check the clutch pedal adjustment, should be 7" from foot rest to bottom of clutch pedal. This is adjusted by the clutch stop adjustment bolt. Next check clutch free travel should be 1/2" and is adjusted by loosening the 2 bolts on the clutch pedal and putting a wrench on the squared part of clutch shaft and turning.
There is an inspection plate on bottom of clutch housing that can be removed to check the throw out bearing. If the transmission clutch works after doing clutch adjustment and the PTO still chatters there is another more involved adjustment. So try clutch pedal adjustment and post back.
Hope this helps