So it's upgrade time for me.......

So it's upgrade time for me debating on the razr hd or maxx hd, can't seem to make my mind. what i am curious on is if the phones are identical in size and if some of the parts are interchangable. my brother has a modified razr with the maxx chassis, battery and battery cover; curious if its possible to do the razr hd with maxx hd chassis, battery and battery cover or if i get the maxx hd if i would be to change out the black front with white front from the razr hd.