How much oil should my Six be leaking?

Oil leaking from head gasket to outside is very unusual, though that was the problem with the early 2.4L engines. Most likely source of your oil leak is the valve cover and/or the spark plug tube seals. The later were on earlier slants, I know in 1969 (had one) and I think your 1971 too. Leaks are so common that wags here call those "drool tube heads". You can still buy replacement rubber seals cheap, ~$1 ea I recall at rockauto.com. If those ever disappear, I once used O-rings on mine. Be sure to take the metal gasket off the spark plugs (many posts).