Hi, It all looks perfect, so a bit of a mystery to me why it should slip so badly. Check that the tongues on the plates are not binding in the slots in the clutch basket, and holding the clutch ‘out’. That includes the inner tongues where they engage with the slots in the clutch drum. Also check that the cable is properly adjusted, with some free play at the handlebar lever end. I can see that the clutch retaining nut is tight, as the tab washer bent over the flat on the nut is visible in one of your photographs. Make sure that the outer edges of the plates are not binding on the inside of the drum. I don’t think that you have corks in the friction plates as they look more like the composition ones with bits of wire in them. This stuff was called ‘Neolite’ or something like that, and note that if the plates are original the stuff will contain asbestos, so take the appropriate precautions when handling the plates.