When you say thick balancer are you talking about a external balanced engine balancer? All the 413's I have ever known were internally balanced. I have a 413 M/H engine from a 71 and it has the forged crank balancer. I just recently put a 74 440 from a M/H in a 86 pickup and it worked fine. What year engine are you working with and does it have the extra cooling passage heads and water pump housing?