I can't say I'm 100% on this but I remember 6 quarts be the min. I have been told by mx's and owners that the plane with blow out a quart or so eventually. Meaning that the plane is oil capacity is stable around 5 but can get to 4 and will be fine.

page 3 has some oil info.

http://saintlouispilotservices.com/y....246151541.pdf