The adapter is a Chevy plate that I milled to fit the Y-block intake, then I milled it to fit the Holley Street Avenger 600 cfm carb. The yellow engine is a 1954 256 with only 41,000 original miles. I am taking it out of the Mercury and storing it. I am replacing it with the other y-block it is a 1957 Thunderbird 312.