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3. The lifter valley offers four additional head bolt bosses to aid in clamping the heads to the block. We installed a Stef's valley screen kit and magnets at the corners to keep any valvetrain debris from making its way downward. We also had Brodix machine the lifter bores for larger 0.903-inch-diameter lifters, when we ordered the block. We chose the large-diameter lifter body because it allows for a large-diameter roller and axle, which in turn means more load-carrying capability to withstand the high valvespring pressures we'll be running.