I agree with others on checking cranking compression and fuel pressure.
What heads are on the motor? Did you try another carb? Is there a shop towel in the intake
It took forever to properly tune my 357. Don't get discouraged, keep at it. Clevelands are a different animal, especially 4V heads. Does your engine/tuner guy have cleveland experience?
There is something fundamental being overlooked somewhere. That cam and cubic inches should be absolutely ripping the pavement.
Make sure about fuel and spark before you go tearing into it.
Good luck,
James P.