Sorry to hear about your disappointing experience. I would think any decent mechanic that has experience with carbs should be able to tune your engine assuming all the mechanicals are in good order. Is the exhaust actually visible, gray or whitish/gray or black during idle? Is the engine rough, at the mentioned RPM range, during acceleration and deceleration? Is the vibration consistent? Is the distributor set up correctly? My experience tells me that moderately rich doesn’t cause vibration as you described. If you think it’s the carb tuning I would contact the carb manufacturer for a recommendation on jetting for your engine configuration. They should be able to get you close or at least drivable. Is the damper new?
Being accustomed to modern engines with EFI and cats, old school engine exhaust is a real eye burner.
Mike