55-56 fenders will fit fine, the difference is in the grille area. you can use them as-is if you are willing to use the 55-56 eggcrate grille. if you must have 57 grille then you need 57 fenders. there is a flat-spot/notch and hole on the 57's to accept the different grille.

i know this, because I have the opposite problem as you, as i describe in this thread:

https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=687143#Post687143

Last edited by tomctomc; 10/21/2010 12:14 PM.