Grab your grinder and grind the sweep handle off on each side of the nut, tap the nut with a hammer and it will fall thru.
I enjoy saving these old sweeps and use a good rust penatrant oil, pliers and a propane torch. Soak the sweep nut in the oil for about three days and try to turn the screw with the pliers if won't budge time to pull out the torch. The turns have got to be miniscule back and forth or the screw will break off. Soak all parts in evapo-rust for that brand new look. Good luck next time.
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