Ignitions systems and charging (alternator) systems are functionally separate. Voltage regulators and alternators are close-coupled units within a single (sub)system. Loose coupling between separate (sub)systems allows a degree of mix-and-match. Within a (sub)system, tight cohesion mandates all components work together precisely.
Ramblers (then Nash ... then AMC) always had a tendency to be cobbled together from different sources. I recall one person bitching about having to go to three different dealers to get parts for his Nash sedan.
