Two distinct differences between your run in stand and the car are the fuel system and electrical system. I would stop changing things on the engine and concentrate on the car. The issues will be within the chassis electrical, fuel delivery, or vacuum systems.
I now have the new 383 in the car and it runs just as terrible missing, surging idle, won't stay running, etc... Also the starter makes an evil screeching noise when it fires now too. Sometimes it won't eve kick over at all.
Out of all of your posting, this is the area we need more clarification on with specific times, sequences, and events.
Starting at the begining of a start up sequence, if sometimes the starter won't turn over, this could be a faulty ignition switch, bad wiring in nueteral safety switch, or bulkhead connection problems. Screeching during turning over, inadequate amps for the starter, intermittent electrical signal to key componets, bad starter motor, bound up starter motor, or someting not bolted on correctly to cause excessive loading on the starter. On the idle, do you find yourself having to turn it up to keep it idling and unable to dial in the mixture at lower rpm? This could be a vacuum leak in the brake booster or the heater controls. Missing I would look at the harness wiring and connections between the ecu, ballast, and coil. I'd also verify the ECU wiring is correct into the harness. Again, more potential bulkhead issues could also contribute to this.
