These bar clamps could be used to hold a threaded assembly with a shaft seized inside it, their length provides valuable additional leverage.

IRWIN QUICK-GRIP Light-Duty (63kg) Mini (300mm) Trigger Clamp, Twin Pack, T54122EL7
5.0

WORKPRO 305 mm Ratchet Bar Clamp Set, 440 mm Spreader, Quick Release and One-Handed Clamp, Ideal for Woodworking and DIY Projects, Max 68 kg Load Limit, 2 Pack
5.0