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One thing that makes the 289 High Performance V-8 different from 289-2V/4V engines is this slide-on counterweight, PN C3OZ-6A360-A, which goes between the timing sprockets and No. 1 journal. According to Bob Mannel's small-block V-8 book, this counterweight is pinned to the C3OZ-6306-A crank sprocket. It is virtually impossible to install this counterweight incorrectly.