440 power gains/ aluminum head advantages?

If it does turn out to be suspect cam timing and it's retarded, when you correct that, your converter will likely flash higher. I previously noted my 440 Charger in this thread. Like you said you have, mine is also an old TCI 10" converter - the "Street Fighter" they called it. Mine flashed to 3200 rpm so you might get there too (or higher). It was good enough for 12.50's shifting at 6200 rpm with that old 292/.509 purple cam. And that with a 750 vacuum Holley.

There's no reason yours can't do that or better - keep digging! You'll find it soon.