I used Keith Black Hypereutectic # KB278 on my Superbird 440-6bbl engine - however this was with stock open chamber 906 cast iron heads. These have a +0.200" dome which must be custom machined to get the correct quench clearance of ~0.040". This quench greatly increases swirl in the combustion chamber and thus significantly reduces the risk of detonation.
KB performance cast pistons are manufactured from a 390 alloy of aluminum, copper and silicon. The structure of 390 alloy gives superior wear resistance, 15% less thermal expansion and increased thermal barrier properties.
They are then heat treated with the T6 Heat Treatment process which increases the strength of the alloy by as much as 30%.

These pistons thus have a very tight piston-to-bore clearance (0.002”) which significantly reduces piston rocking and thus improves the ring seal.