Could be timing too retarded, could be idle set too low on the Holley.
If you have a helper, have them keep the motor running at around 600 - 700 rpm, disconnect & plug your vacuum adv (if you're using it) & see what your timing is set at. Start about 14-16 deg btdc & see what the motor does after that.
No helper? Temporarily turn the idle adjust screw in on the carb to keep the motor running (same rpm as above) & check timing.
It's a start.