Before anyone makes any changes some clarification may be needed - Joe Frazer, are you referring to a Delco 6 volt starter handling 12 volts? Seems to me my dad had a'53 J that was converted to 12v and I think he left the 6 volt starter in it and as you said, it was OK. That being said, I know for a fact 12 volts will blow an Autolite starter in the earlier cars - it did so on my '48 Frazer when we tried to jump it with 12 (and only left it on momentarily) - it rips a metal ring apart inside it. Didn't hurt it electrically though but after having done that, I spoke with John Haller and Keith Zimmerman and both told me they had the exact same experience when they tried to jump their early cars with 12 volts - rips that metal ring in the start apart. So, I guess my question is, does it matter if it's Delco or Autolite? A '51 would be Delco but Joekeys2010 I believe, is Autolite.
And by they way, regarding the ignition components, points and condenser can handle the additional current but the coil, probably not.