Been playing around with this, pulley is from a VS commodore harmonic balancer. This is just pushed together with a bit of interference at the moment, would need to be silver soldered or brazed together as the pulley is cast iron. Might see if I can chase down a steel pulley so I can get it spot welded on.

have you tried parting the balancer and using the center 3 spoke hub coupled with a center adapter, which then can bolt to the crank with the fan possibly.

otherwise there are aftermarket billet balancers for commodores.

A centre adapter would work but I didn't want to disrupt the airflow with the spokes and hub. I'll keep looking for something more suitable, next time I'm at the wreckers.