Use two ballast resistors in series, and see what the voltage is at the coil with the points closed, and/or with the engine running. You might be able to hide one or both of of the resistors somewhere it's not obviously in sight, if you want to have a stock-appearing underhood area.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!