The only time you'll see voltage drop at the coil is when the points are closed and there's a ballast resistor between the ignition switch and the coil. Points open- - - -you should see full battery voltage. Points closed, you'll see approximately 9 volts if the points are in good condition.

Try checking the voltage at the distributor side of the coil with the points closed. It should be almost zero. If the points are dirty or burned, you'll see a measureable voltage upstream of the points, which will cause the input voltage to the coil to be incorrect.
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!