Turbo 383 in a A-body Barracuda

Mad Dart said
Do you have a goog ground strap from the engine to the body of the car? I hook my leads directly to the battery. You may be loosing ground at cranking is another guess. Try grounding directly to the battery.

Yep!
One from the battery to the engine block, one from the block to the firewall and one from the block to the wiper motor stud.