without going into the details, i'll say that as the question is worded, the answer "NO" there is no reason why you can't. but "yes" there are plenty of reasons why you shouldn't and is unlikely to work well or for long, if at all.
the details are contained in many forums on the subject of the 6v to 12v conversion process on Fords and many pre-1950's cars from all over the world. they can be found by googling. they can also be found using the search tool on this site. good luck.
