houstonmustang

I am in the process of taking the pulley off to see if the compressor is gone or not.. Is there a special tool to get the square nut off under the cover?? I'm afriad if I use any kind of clamp i'll strip the metal due to all the 26 years of corrosion.. What A/C compressors can get swapped into a 280zx 1980?? I've looked around but can't find a 1980 model.