ANCIENT HISTORY: I played 6-Man Football in the mid 1950's.
From an old notebook - here is how WE played the 4-2 (vs. Single Wing):
----------------O
------------O-----O
--------------O--C--O
-----------E-S--C----E
--------------H-----H
4-2:
The extra man in the line (Safety) is used to give strength to the strong side. If a pass develops, two men from the line should back out of the line, and the two remaining men should rush the passer.
The Strong-side End & the Center (Nose) should rush, but the Weak-side End and the Safety should play a waiting game. The two Backs should play a little deeper than the Halfbacks do in the 3-2-1 defense, and they should be behind the Ends rather than outside of them. If a pass play develops, each Halfback should cover his zone and not let the end on his side get behind him. The extra man in the line (Safety) should drop back and play a zone behind the center, and the Weakside End should drop back into the flat zone.
This was all I could find ion that old defensive book. We only used it that one time, evidently.