My instructions say that the head gasket that comes with the 95 CI BB kit take care of what the head-to-cylinder O-ring used to. It also says that if the O-ring is installed, the engine will be seriously damaged. Sounds pretty scarey to me, so I left the O-rings out. I've got about 4,000 miles on the kit, and it seems to be running just fine, with no external oil leaks. It did seem kind of unnatural to leave them out. But it's what the MoCo Dr. ordered.
The cometic gaskets (and others) have a raised ring on the gasket in the area where the ring would normally go (see attachment). This eliminates the need for the o-ring.
Read the instructions that come with the head gasket!