Sounds like it needs a serious tune-up. A few questions to start, so the really smart guys here can weigh in.
Initial timing, and total timing (no vacuum advance)? Is the vacuum advance connected to manifold or ported vacuum? Brand and size of carbs, and jetting? any other particulars that were changed or added to the crate motor. When was the motor purchased, and built? There were some issues with crate Hemis before, so this may be important.
