The belt tensioner should be spring loaded and apply constant pressure to the back of the drive belts - it should not change position when the clutch pedal is pressed.
The pins are probably not worn much if any - I believe they are made of a harder steel than the yoke. I would not weld around them unless they are worn - you can try the pins at the ends of the slots to see how they fit as the end areas of the slot are not usually worn. If you look at the attached pictures you can see in the first picture where the pin wore the slot area with years of the clutch being disengaged and engaged and in the second picture you can see how the slot should look after it is repaired.
Should the pins and clutch yoke have movement side wards?