Not even close. The 55 seat is much higher. 61 seat is lower to the floor, cushion is thinner, built differently. You would be better off with 60-64 seat
I didn't even know that a '55 had a split bench let alone a '61. Are you talking about the seat part being split or just the back being split? If it is just the back that is split then that is the standard bench for a two door.