You don't need to change the balancer. As has been said you can slot the offset hole in your LA pulley if it has one. The magnum balancer ring is thinner but the inner hub is in the same plane. What you may need to do is fab some brackets for the alternator mounting though as the head bolt bosses at the ends of the heads are not the same. You could however use the entire front accessory drive, The alternator and power steering pump will still work with a earlier wiring harness. Did you plan on using the TBI setup?