Does this engine have mechanical / vacuum advance in the distributor?

What brand of distributor?

If Bosch, does it have the same small diameter distributor cap as a 4 cyl engine?

What type of trigger is in the distributor? ( points , hall effect , reluctor coil , optical )

If Bosch, you might be able to swap distributor parts from other cars to make a hall effect , reluctor coil trigger.

You might be better off using the distributor to trigger a more modern " can buy at any decent auto parts " ignition module / coil then open up the plug gaps 0.005 or 0.010 over stock.