No problem, as long as your 6V system is up to snuff. Pay close attention to cable sizes and be sure the connections are clean and tight, and keep them that way. There's very little room for voltage drop on a 6V system, particularly in the ignition.
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!