Need some advice

The 3 speed is OK at best. Worry about that later.
Install a set of gears. The 3.91's mentioned should be good.
Everything else is in the tune of the engine. The set up looks good for a nice street car.

I'm not really a fan of the Orange box. I like the Chrome or FBO box. Recheck and curve your distributor. Make sure your carb is well tuned. Primary and secondary.