More power from my 360 Duster?

Nice car.
To break the damper bolt loose: Carefully put a breaker bar on the bolt and rest it on the driver's side frame rail. Tap the starter (ignition disabled!) Bolt will loosen. To torque it on: Wedge a piece of wood in the ring gear. There's a will, there's a way! Be careful.
Is traction an issue now? Even if it's not, it will help to analyze changes as you go to have consistent hook. A shorter tire improves gear ratio, too.
Maybe you can find a whole different pumpkin. If it's just for "fun" use, get a ratio that's ultimate for your combo. As mentioned, you can swap them quickly. I used to change from 2.93(road trip) to 3.91(orig) to 4.30(track).
Also mentioned, but worth re-iterating; be sure the carb secondaries are opening quickly. Can be a lot there. The more convertor and gear, the looser they should be. Make sure you get full throttle out of the pedal! (Been there, done that!)
Timing set? I think about 35* total is good. If your balancer isn't degreed, I think 35* is 2 1/8 " from the TDC mark. (clockwise) Check that measurement, it's been a long time!
I also like the cam, compression and port/gasket matching ideas.
I like to make what I have work before I change things. Being accused of having more than you're claiming is a great compliment!