There is a 6V conversion of a GM 10-SI alternator that's virtually a bolt-in swap. Just fabricate a bracket that aligns the belt pulleys properly and bypass the charging system wiring at the voltage regulator. That "high voltage" ignition system modification is a solution in search of a problem, as long as you're willing to do a little regular preventive maintenance on the original ignition system.
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!