340 - This thing should run better

Do you know how to properly set up points (reading dwell, not gap?)? Did you degree the camshaft? can you get cylinder pressure readings?
If the heads had no valve job, and the ignition is not perfectly set and tuned (as far as timing curves & initial) it may feel doggy because you don't have headers or a convertor.
I would get it running better before you buy anything "downstream" in the power train. Fix the cause, not the symptom.