First off, check to be sure the carb to manifold bolts are all present and tight and intake to head bolts are all present and tight. If you have power brakes, pull the hose and cap the port at the vacuum source. Pull the hose to the PCV valve and cap the vacuum source, or pull the PCV valve and seal the hole in the valve with duct tape. No other vacuum leaks would be big enough to cause this issue.

Then start the engine. If the engine won't start or won't stay running, you've isolated a vacuum leak. Plug the hoses back in one at a time to determine the source.

If the engine still races on, continue with the choke. On the passenger side of the carb is the stepped cam for fast idle. Use your finger or a screwdriver to ensure it is on the lowest step. Once on the lowest step, back out the fast idle screw on the choke. You should be able to reduce the idle speed enough to stall the car, if you have backed out the curb idle screw as you've described. Once the car will not stay running, set the curb idle screw to the recommended setting and start it. Check your vacuum with the distributor advance disconnected and plugged at the vacuum source.

Once you can establish curb idle, you can go back to resetting the fast idle. Chances are you will find either a bad choke vacuum pulloff or a vacuum leak.

As long as your wiring harness is unmodified you have a resistance wire in the harness. The coil cannot cause this issue.