Headers and an updated exhaust would be a good choice, also look into recurving the distrbutor. Depending on how much money you want to spend and how far you want to go into the motor; a matched cam, intake, carb and even cylinder head swap would be something to consider. There are a number of companies that offer matched packages That would have been good to do when it was rebuilt, but still not too late if you really want to do it. Another choice that might be worth considering is taking the original motor out and sealing it up nicely in case you want to put it back to original, then putting a good strong crate motor of some kind in. Another instant performance boost would be lower rear gears and a looser torque converter. Those will make it less fuel efficient for sure, but sounds like this is not your daily driver.

Good luck

Pat