Keith actually covered it pretty good.
them 3 cyl's used a 6v coil and a resistor wire. the r-wire was in the run circuit. at startup, the 6v coil was powered by full bat votlage.. or whatever was left after the starter took it's share.
there are various ways to do it. old fords used a thermall sensitive resistor.. newer setups could use a solenoid with a bypass line on it.. or simply a different tap off the key switch, etc.
newer oil potted coils can handle heat disipation better and thus can be run a lil hotter that an older dry or hard epoxy or even older hard tar-like potted coils.