A significant difference is the open drivetrain. Both have 3.90 differential but if you intend to keep the rear axle and swap gears you can go with 3.38 while the 54 swap is for 3.55. The rear springs are the same overall length but the "center" hole is located differently. The 54 rear spring mounts to an offset rubber insulated "projection" off the axle while the 55.1 bolts directly to the axle. In 54 the grill background color is white but is black on 55.1.
