Tiller blades won’t turn

I would take the pto shaft off then turn the tines by hand and see if the shaft coming out of the gear case turns,my tiller has a slip clutch between the pto shaft and the gearcase the side of the slip clutch toward the gearcase there might be a grade 8 bolt that can shear but it holds the clutch in place mainly . If your does not have a slip clutch do not use grade 8 or 5 bolt ,use a 2 or 3 , and I think they are typically 1/2″x3″