The bolt on cover has a couple uses. It lets you get in the trap area to clean but more importantly it is for windage. As the crank turns it causes wind inside the motor and this can be so much so that it causes the oil to ride up the sides of the pan and come in contact with the crank. If this happens you get spraying everywhere plus it aerates the oil. This is suppose to help keep the oil in the sump. This is a guess but I think the "box" is 4"x4".
Jay
422motorsports.com
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