Do you have a parts manual? There is an exploded view of the clutch assembly in it.
My guess is that it sat for quite awhile without being started (way more than a month), the pressure plate and disc stuck to the flywheel so much as to cause one of the roll pins in the cross shaft to shear. There are two of them. If you are lucky it's the one on the outside, if not, it's the one on the inside (holding the yoke) and the engine will have to be removed. Sorry.
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