Maybe I've learned a good lesson . . .

I'd think there is some potential in the torque converter. Call a place you can talk with about the weight of the car, gearing, the engine and cam. Even Turbo Action (which I think of as off the shelf) will ask you about that. Or at least they used to.

My opinion, and its just that. Exhaust tubing is a little big and could be hurting low end. 2.5" Muffler size is fine.
Do some performance tuning. Measure the timing curve. Then make some small change and test out.
Same with the carb. Document what its got. make a change and test that change. For example, if changing the MJ, that's a full power change to be tested at the strip. If its a rod/mj, that's high speed cruise change to be tested on the interstate. The part throttle acceleration is hard to test but will work out when the steady state stuff is tuned.