1954 bel air

hello to everyone out there, my ? is I'm using a 1956 bel air rear end on my 1954 bel air. and plan on keeping the original leaf springs, shackles hardware ect, for the time being. the rear is the correct width 60". but the tubes are bigger than the original, would the spring mounts that go on the frame have to be moved back, so the rear can be centered  or I don't need to do any of this and it bolt's right up. I'm getting to many people telling me different things. don' t know please help. any one thanks 4 your time............kingofkarz