[rotorwrench]

I don't know about the GM & other makes but FoMoCo used the same coil well up into the 12-volt era. The 12-volt vehicles used a ballast to control the amperage to the coil where the 6-volt vehicles didn't need one. The late type (1948/49 & later)round can coils were an improvement in technology and could take more heat than the old plastic covered iron core coils could.