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This particular block is the prototype for the Butler aluminum block program. Its sleeves feature a 4.5-inch od and a .125-inch wall, which are press-fitted and have a step at the top and flattened edges to meet with the adjacent cylinders. They will accept an O-ring or receiver groove for superior cylinder sealing. Block deck height measures 10.22 inches. The block weighs in at 125 pounds with the sleeves installed, compared to about 250 pounds for an Indian Adventures cast-iron unit.