[rotorwrench]

Dwell can vary some and not be a problem. As far as timing is concerned, the point at which the points open is very critical. The point that they close is less so. Dwell is important on the older coils that needed all the time they could get to build up the flux for the next collapse of the magnetic field. On the more modern coils with epoxy insulation, the dwell time can be shorter but not by a lot. Battery ignitions with points & condenser were generally always just good enough to do a decent job. Now days, there is a coil on each cylinder with electronic breaker control. They can be a lot hotter than any of the old stuff could ever be.