No, i was actually going to keep both the same diameter,with 63mm O/D piping and then a 63-57mm reducer a the cooler, why is there a benefit to have the cold side reduced to say 57mm?
I think he just got sent the wrong size pipes thats how it came about on his, i would do it how you said mate 63-57mm at cooler you will have to let us know how you get on with it, have fun with the bumper again bet you can take it on and off with your eyes closed and 1 hand behind your back now id look into getting it made quick release