"o" ringing the block , "o" ringing the heads , copper head gaskets the reason to "o" ring the block instead of the head is it makes installation easier, and you dont have to worry about the "o" ring falling off the head. copper gaskets are good to use, and reusable, but i wouldnt run them on the street except as an exhaust gasket.
Yeh I just read they were notorious for being leaky on street cars. I guess the extra expense probably isn't worthwhile. Perhaps for dedicated race engines with high cylinder pressures that get rebuild OFTEN, but for street they sound not very inviting.