Duraspark III took over more of the timing control and was a stop gap system between the old mechanical timing control of the duraspark II and the fullly integrated control of the TFI system.

No. The main advantage is less maintenance since it doesn't have mechanical points. The dwell remains constant due to no points and rubbing block wear. The duraspark II coil may be a little hotter than the points coil, but not much.

 

Plug gap is simply a function of nominal secondary voltage - the plugs have to be gapped according to what the system generates. Duraspark II specifies a wider plug gap than points because the coil produces a higher secondary voltage due to a higher-output coil, as well as longer, more consistent dwell.