First, Welcome to CHR, Tegguy! This is a great forum with lots of people who know lots of stuff! I don't know what your plans are for this car but if you're going to restore it back to somewhat original condition, you might want to enhance your experience by checking out Dedicated To The Ford Thunderbird Car Hobby. I haven't actually been on their site but from the homepage it seems like they would have a lot of info & resources for someone restoring a 55 Tbird. Otherwise, I'm sure somebody will come along who knows these old birds well enough to answer your questions. Again, welcome to CHR and don't be afraid to post up some pics of the car so we can see what you're working on.
Randy