Check the voltage at the coil + terminal with the engine running. If it's more than around 9 to 9.5 volts, you'll need more resistance than the OEM ballast can provide. I'm not really sure the MSD coil will work properly with voltage that low.
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!