Is there a way to exchange harmonic balancers and not have to rebalance the engine? NHRA requires a SFI rated balancer so I will need to change mine on my BBC and I'd like not to have to pay the $$ to rebalance the motor. Any suggestions??

I'm assuming this is an externally balanced motor? Take your old and new balancers to your machine shop. They should be able to match the new balancer to the old one.