Welcome to the site. You'll find a vast amount of knowledge available here.
I also have a 55 which I've owned since 1967. When I first bought it it had 6v throughout. I managed that for many years but did a complete replacement and upgrade to 12 volts. A 6v system is manageable but pretty difficult in todays service & parts world. It will take your time and patience to learn and understand it, but it is possible. Today, I would only retain that system if I were building a Concours perfect 55 bird. The Mallory will work great with it.
You didn't state your location, but weather conditions are tough for starting on 6v. If you do want to keep that system, The Barn website may have some good info for you on some tricks and tips to keep your 6v in good shape. Good solid grounds are what first comes to mind and an engine that runs cool for restarting. Good luck, and enjoy your T
Bird!

       A  L  A  N   F  R  A  K  E  S   ~  Tulsa, OK