What gain will I see in my time slips

For sure, if the converter sucks....... the car just won’t put up a good number.

But I think this is converter number 2 already(I realize that doesn’t mean it’s “right”).

As the guy who has been playing on the dyno for over 30 years........ that’s where I would have started.
After the first few tweaks, and the car was still way off of the estimated performance, I would have had the motor tested locally by a reputable dyno service....... to see if the performance and the dyno numbers coincide at all.
Plus it would give you an idea of how well the carb was working, along with the shape of the power curve...... which helps with converter selection, shift points, etc.

In the event the dyno numbers are a pleasant surprise........ you then know you don’t need to spend any $$$ on the motor, and can concentrate on other areas of the combo.