as far as i remmber my buddies 35rem is a CS. the C i remmber does stand for the stock wood. the S i beleive was that model of that year or that run. it is the same 20" barrel and has a smaller tube to only fit i beleive 4 or 5 in the tube.
it was made in the late 60' s through the late 80' s.
those are nice guns. they don' t make them like those no longer. does it have the pistol grip cap black with a little white ring on her?
you migt want to find out more on marlin' s website they know almost everything you ever wanted to know about the marlin