Spiny Norman said:
(These LDs often (more often even) also had 'matrixed' 4 channel surround (stereo + center + rear mono) but it's debatable if the quality of that is good enough to warrant capturing - it's not as good as 'discrete' 5.1.)
Take a look here: http://originaltrilogy.com/forum/topic.cfm/Restoration-tips-HD-matrix-surround/topic/17967