Here's one of the things Quarter Master makes easy when racing crates. Like all old Chevy 350s, the 604 is externally balanced. General Motors uses a balance weight on the damper to take care of the front of the motor, but adding the proper balance to the back normally requires using a heavy stock flywheel. Quarter Master solves this problem by including this balance plate that will sandwich between the flywheel and drive hub. The holes in the plate are clocked along with the crank mounting holes so that they will only work one way. There's no worry of misaligning the balance plate and tearing up your new crate engine.