These are Fel-Pro part numbers. I know the difference is the 1011-1 is metal lined and 1011-2 is copper lined. They list the copper one as the head gasket set for late model 5.0's (83-95 I believe) and the metal set as early blocks. I mistakinly picked up the metal lined ones for my 91 5.0 motor that will be recieving some AFR 165's soon. AFR lists both gaskets as acceptable. Now the only thing I could think of that could go wrong is the the water ports in the gasket are wrong and could cause my motor not to cool right when I fire it up. Does anybody know anything about this? I'm thinking old 302 water pumps where clockwise rather than the 5.0 being counter clockwise causing the different head gasket designs? Can someone help me out?