RE: Corvette Aluminum & Fast Burn Cylinder Heads
Starting in 1988 with the Corvette Aluminum heads, and continuing though today's Fast Burn heads, the exhaust ports have been raised, without moving the original bolt pattern. The result is the exhaust ports are offset. Therefore, using a standard Chevy flange will result in a port mismatch, thus causing disruption of the flow of the exhaust gasses.