I just ran into this issue, I have a 2001 Cobra, and previous owner swapped in an Aluminator block. I just tried to use a Felpro oil filter adapter gasket, it happened to be blue, and it leaked all over. The car came with a red one, so I put it back in, no leaks. I’ve been staring at these for an hour. Can someone help me see the difference?Don't get hung up on the gasket color - I have seen them in orange, red and blue. The FelPro kit I recently picked up for an upcoming Aluminator build has both gaskets, and both are blue. You just have to know that the one with the smaller opening is for the iron block and the larger is for the aluminum. In the pic at the very top, the small one is actually orange and the large is blue, but they are also easy to compare visually even if the color is the same for both.
Here is the block side: