Yes, a 6V generator can produce 12V- - - -No, it won't last long. If it was that simple, why would Delco-Remy and a bunch of other manufacturers have gone to the trouble and expense to totally re-engineer their systems when the swap was made to 12V in the mid 1950s? A bunch of toy poodles can probably pull a sled across Alaska with enough "encouragement"- - - - - -so why would the competitors in the Iditarod race use huskies instead?
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!