Aluminum heads mean nothing. The only change is that they make less horse power for the same static compression ratio.
All things given equal, they require the same specs as their iron counterparts.
Mine has aluminum heads and the engine likes 16 degrees initial. It doesn't respond to 34, 35, or 36 degrees. Drag racers reduce total timing to raise top end speed through the lights.
I would immediately go to at least 14 degrees. Then you need to close the throttle to lower the rpm and to reduce or eliminate run on.
One of the things Ford needed to do in the mid-70s to reduce run on was to install a throttle solenoid. It enabled essentially a two position throttle. Don't be surprised if the thought occurs to you.
If you have to go that way, there is the Boss 302 solenoid and bracket for the Holley carb. When you switch the ignition off, the solenoid collapses and closes the throttle 100%.
If you wind up with low idle vacuum, i.e., under 14 inches, you may need to use one anyway because of your particular combination of cam, carb, intake, etc.