Slant 6 Turbo 68Dart Project

Just a thought, I don't know if anyone mentioned this....

The way you describe your cranking almost seems like there might be a great deal of fuel in some of the cylinders causing a partial hydraulic. It might be worth your time to pull the plugs and spin it over, and perhaps drop the oil out of it. After pushing all that fuel through the carb vents this is a possibility.