How much improvement will I see?

Once you get the new converter in, disconnect the secondaries on the carb and tune the primary bog out from a dead stop hitting it to the floor. Then, load it to about 1500, and smack it. Then 2500, smack it. If it isn't bogging in those conditions, next step.

Connect the secondaries and do the same thing. Trying to do both ends at once is a pain. Make it easier.

You also need to find out what your car likes for launching. Some cars like to be loaded hard where they almost push through the brakes, other like to hit the converter like a ton of brick from idle.

This test engine has a bit more compression and larger solid cam in it. Just as a reference to the intake manifold comments and converter choice (hopefully it's the highest they can stall it). The cam in your engine may get you to about 5800 making power.
An Air Gap is going to pull through the range faster than the Torker 2. The Torker in that test had some plenum work and port matched. TQ/HP crossover doesn't happen until 5000 rpm.

https://www.hotrod.com/how-to/mopp-0108-dyno-testing-small-block-intakes/