http://www.nissansilvia.co.uk/vbb/showthread.php?t=3707
for Z31 sub frame bushes, some say leave in the metal outer ring, some say remove it, all we know is, try it with the ring in, then remove it if needed.
if you have lowered spring in the rear, then you shouldnt need compressors to remove them, if you have std springs in, then jack up the rear onto axle stands, then put the jack under the spring and jack slightly, undo and remove the lower shock bolt, and then lower the jack to release the spring.