quick question, basiclly does the 4 speed gearbox have a crank shaft sensor ?

The gearbox does not have a crank shaft Presume you mean the 4 speed models, but yes it depends on the engine not the gearbox. All later 300s with the renix/bendix computer ignition (module with the built in coil+vacuum sensor) use a flywheel sensor. Approx 1984 on I think.